We Keep Coding

Visual Studio 2017: References are mentioned not being built while they are already built

I'm working with Visual Studio 2017, enterprise version. I'm working on a C# project, depending on several NuGet packages.
One of my references is mentioned being missing (there's a yellow triangle above the icon in the solution explorer). When I double-click on it, in order to see its contents in the object browser, I get following error message:
This project cannot be viewed in the object browser because it is unavailable or not yet built.
Please ensure that the project is available and built.
You might think: "just restore the package (it's a NuGet package) and off you go", but the problem is that the message makes no sense:
In another project, I am using the exact same NuGet package as a reference, there everything is fine, and when I do a file/directory compare between that other project and my current one, WinMerge mentions both being equal. (Not only WinMerge, I also did a checksum comparison)
So my question is: what's the source of Visual Studio's This project cannot be viewed in the object browser because it is unavailable or not yet built. error message? What's the source of the yellow triangle in Visual Studio's solution explorer (for NuGet packages)?
Edit (added: Visual Studio version)
For your information, I'm working with Visual Studio enterprise 2017, version 15.9.36.

In the meantime I've found a workaround: I remove the references from the project and add them again, and it seems to work. Apparently there's some instability in Visual Studio reference handling.

Visual Studio doesn't find my references and they are already here

I'm coding a C# application. When I compile my code, I have hundreds of errors about some missing references and packages that I installed. Visual Studio indicate that it doesn't find them, but when I see the NuGet packages, they are all there!
This problem occurs after synchronising the project from git.

How Do I Make the Builder on Visual Studio Online Restore All NuGet Packages?

I have a solution in Visual Studio 2015 that uses several NuGet packages. When I build in Visual Studio 2015, the packages are restored properly and the build succeeds. However, when I push that same project to Visual Studio Online, even though I have "Restore NuGet Packages" checked, the build fails because MSBuild cannot find the referenced binary.
I have looked at the build log and see that my packages are all being restored. Why, even though the package is restored, is the referenced binary not found during the build?

I found that the problem was not in the NuGet package restore, but in the way that the hint path was written in my .csproj file. To the fix the problem, change the hint path to point to the solution directory using the $(SolutionDir) variable.
For example, the NuGet restore pulled the Microsoft.WindowsAzure.Storage.dll binary, but it could not be found on the build of the project. To fix this, I had to open the .csproj, find the reference to the dll, and change the path from
..\packages\WindowsAzure.Storage.6.1.0\lib\net40\Microsoft.WindowsAzure.Storage.dll
-- to --
$(SolutionDir)\packages\WindowsAzure.Storage.6.1.0\lib\net40\Microsoft.WindowsAzure.Storage.dll
By using the $(SolutionDir) variable, Visual Studio Team Services was able to find my referenced dll and build my project properly.

You might also consider checking if the file packages.config, which surely resides on you local system, also gets checked in and is under version control.
First, you might want to see if it's present at the build server (image below is from VS Team Services but it's the same general idea in on-site environment.
Secondly, verify that the file's under version control. As a test, see if it appears under Pending Changes if you add a package.
I made a project with a working build start to fail when I added nUnit. Then, as I checked in the package.config file, it started to restore the packages on the server. When I removed the file from the server, the builds starter to fail again. Details are described in this post.

Visual studio doesn't support specific csproj file

I am getting this error when I try to open the solution file of my project. The solution is 2012 file (checked using notepad).
If I click on Ok, The solution opens up except for one csproject which does not load.
I get a migration report in UpgradeLog.htm file, with the following error for the project which failed to load. Could not figure out much from it.
Error:
The application which this project type is based on was not found.
Please try this link for further information:
http://go.microsoft.com/fwlink/?prd=12395&pver=11&sbp=ProjectTypeDeprecated&plcid=0x409&clcid=0x409&ar=MSDN&sar=ProjectCompatibility&o1=82b43b9b-a64c-4715-b499-d71e9ca2bd60
Does the upgrade report mean that it is a project from previous version of Visual studio? It does not open in Visual Studio 2010 either.

The error doesn't say that Visual Studio doesn't support .csproj files at all, it says it doesn't support a specific project type in that particular project file. This means this either isn't your project as you claim, or you are trying to build it on a different machine from the one used to create the project.
Visual Studio uses various elements in a .csproj file to determine its project type. See How do you tell the Visual Studio project type from an existing Visual Studio project and What is the significance of ProjectTypeGuids tag in the visual studio project file. It does this so it knows how to compile your project, what properties tabs to show, what context menu options should be available and so on.
Certain project types can cause this error. Usually they require some kind of SDK to be installed on the machine used to open or build the project.
You should search the web for the GUID mentioned in the error message you show (the value after o1=). You can also open the project file in a text editor and find the <ProjectTypeGuids> elements, which contains comma-separated project type GUIDs.
Then search the web for those GUIDs to find out which SDK or tool you need to install in order to be able to open or build the project.
If you paste the specific GUID from your error message in your favorite web search engine, you'll find Problem solved: Visual Studio / There is a missing project subtype. Subtype: '{82b43b9b-a64c-4715-b499-d71e9ca2bd60}' is unsupported by this installation., where it is mentioned you'll need to install the Visual Studio 2013 SDK. This means that in this case, your project is a Visual Studio 2013 extension.
This is what documentation is for. You should at least put a ReadMe.txt file in your project directory, explaining what the prerequisites for building a project are, especially when it won't open or build with Visual Studio out of the box.

I had this issue when I used Update 5 for VS 2013.
For me I had to click ok and read the next few steps, that popped up. I was initially clicking cancel.
On mine the project was missing Web Tools, so had to reinstall those and once done it was working.
Hope that helps someone.

This issue also appears when trying to import an ASP.Net project into Visual Studio 2015 Express for Desktop, and can be solved by simply downloading and installing Express 2015 for Web - or by using Visual Studio Community/Standard.

I am currently using VS 2017 v 15.7.4. This error came out of no where without any updates on my part. Usually when I have errors like this I just delete the .vs folder in my solution and that clears the problem. In this case that is what I did and the problem was fixed.
Close VS
Delete .vs folder
Load VS
Note: This was for a Xamarin based solution.

I solved this problem by downloading and installing (Microsoft Visual Studio Installer Projects). Close the project then install. After the installation, open your project then reload .csproj file

I had the same issue with VS 2017.
Eventually i solved it by just enable the SSIS in the following way:
1. In VS 2017 - Click on Extensions and Updates in the Tools menu.
Locate the Microsoft Integration Services Projects.
if you can't find it then you will have to install it first.
Click on the Enable button.
Close VS and start it again and SSIS projects are now available.
enter image description here

This (the error that states "Visual studio doesn't support specific csproj file") also occurs when the .vs folder is removed; however, closing and reopening Visual Studio will resolve the error.

Visual Studio 2013 dosen't recognize anything

I opened my WinRT (I'm using MVVMLight) project in Visual Studio 2013 this morning, and found out that all kind of types even system ones are not recognized saying Cannot resolve symbol 'bool' for example, note that the solution builds, executes and works all fine !
C# :
Even XAML :
I tried many things, closed and reopened the solution, cleared Resharper caches, I even restarted Visual Studio and the PC, but still the same problem, any solution to this problem ?
Update 1 : I tried to Suspend/Resume Resharper from Tools>Options and even delete files from AppData\Local\JetBrains\ReSharper\v8.0\SolutionCaches, and now Visual Studio causes errors too :
Update 2 : I uninstalled/re-installed visual studio, and I still have the same problems

If you have any Xamarin extensions for Visual Studio installed, it is a root of the problem. There are some compatibility problems.
As a possible workaround, you may try a workaround, mentioned in this ticket:
Select 'true' for 'Use msbuild to obtain project references' in
Project Properties (Click on project name in Solution Explorer | Hit
F4) for each project in the solution.
At least, it works for me.

If you can build the solution, but ReSharper marks your code in red - you can write the request here and you will likely get a help.
If you can't build your project then it is not ReSharper's problem. Then we need to find out why your build is broken.
It seems that your project to assembly references are broken.
To understand what's happening here with references during the build, go to Tools -> Options -> Projects and Solutions -> Build/Debug and set the verbosity to diagnostic. Then try to build your project and investigate the output windows in VS (or you can use MSBuild.exe from the command line instead). What you need to find in this large text block is "Resolve Assembly references" or "Expand SDK references" task. These tasks should obtain the valid paths to the assemblies your project depends on. Later on csc.exe should be executed with all these paths as parameters.
You can check whether the paths are correct, do they indicate to the existing binaries or not.
You can also create a new WinRT project template and check if it can build. If it cannot even for the clean project template then it is obviously a system problem, I suppose your platform sdk's are corrupted.
Hope this will help.