Error "Metadata file '...\Release\project.dll' could not be found in Visual Studio"

Question

Everyone is correct...try everything...(in order of a little to a lot of time wasted)

1. Do you have bad code? Fix that first.
2. Clean Solution & Restart Visual Studio
3. Remove / Add References
4. Check your build order w/ larger projects and verify
5. Manually rebuild sub-projects
6. Manually copy dlls between projects into associated bin folders
7. Go get some coffee, play some pinball and come back tomorrow...you may think of something else in the meanwhile.

I had the exact same problem. Big visual studio solution with 50+ projects.

All references were added as projects. Project build order was correct (right click on project and select build order).

However when building some of the higher level projects the "root" project they depended on were not built.

The problem was that these projects were not selected to build under the current configuration (don't know how this happened).

To check this select "Configuration Manager" (Build menu) e check if the problematic projects are set to build.

When you say you deleted references to those projects and re-added them, how did you re-add them, exactly? Did you use the "Browse" tab in the "Add Reference" dialog in Visual Studio? Or, did you use the "Projects" tab (which lists neighboring projects in your solution)?

Edit: If you use the "Browse" tab, and manually add the reference to your .dll that is located in the /Release folder, then Visual Studio will always look for the .dll in that location, regardless of what mode you're currently in (Debug or Release).

If you removed the actual .dll file from the Release folder (either manually or by doing "Clean Solution"), then your reference will break because the .dll does not exist.

I'd suggest removing the reference to ProjectX.dll, and add it in again--but this time, use the "Projects" tab in the "Add Reference" dialog. When you add a reference this way, Visual Studio knows where to get the appropriate .dll. If you're in Debug mode, it will get it from the /Debug folder. If in Release mode, the /Release folder. Your build error should go away, and you also will no longer be (improperly) referencing a Release .dll while in Debug mode.

Well, my answer is not just the summary of all the solutions, but it offers more than that.

Section (1):

In general solutions:

I had 4 errors of this kind (‘metadata file could not be found’) along with 1 error saying 'Source File Could Not Be Opened (‘Unspecified error ‘)'.

I tried to get rid of ‘metadata file could not be found’ error. For that, I read many posts, blogs etc and found these solutions may be effective (summarizing them over here):

1. Restart VS and try building again.

2. Go to 'Solution Explorer'. Right click on Solution. Go to Properties. Go to 'Configuration Manager'. Check if the checkboxes under 'Build' are checked or not. If any or all of them are unchecked, then check them and try building again.

3. If the above solution(s) do not work, then follow sequence mentioned in step 2 above, and even if all the checkboxes are checked, uncheck them, check again and try to build again.

4. Build Order and Project Dependencies:

   Go to 'Solution Explorer'. Right click on Solution. Go to 'Project Dependencies...'. You will see 2 tabs: 'Dependencies' and 'Build Order'. This build order is the one in which solution builds. Check the project dependencies and the build order to verify if some project (say 'project1') which is dependent on other (say 'project2') is trying to build before that one (project2). This might be the cause for the error.

5. Check the path of the missing .dll:

   Check the path of the missing .dll. If the path contains space or any other invalid path character, remove it and try building again.

   If this is the cause, then adjust the build order.

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Section (2):

My particular case:

I tried all the steps above with various permutations and combinations with restarting VS few times. But, it did not help me.

So, I decided to get rid of other error I was coming across ('Source File Could Not Be Opened (‘Unspecified error ‘)').

I came across a blog: http://www.anujvarma.com/tfs-errorsource-file-could-not-be-opened-unspecified-error/#comment-1539

I tried the steps mentioned in that blog and I got rid of the error 'Source File Could Not Be Opened (‘Unspecified error ‘)' and surprisingly I got rid of other errors (‘metadata file could not be found’) as well.

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Section (3):

Moral of the story:

Try all solutions as mentioned in section (1) above (and any other solutions) for getting rid of the error. If nothing works out, as per the blog mentioned in section (2) above, delete the entries of all source files which are no longer present in the source control and the file system from your .csproj file.

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I've had this problem before and the only way I've found to solve it is to run Clean Solution and then restart Visual Studio.