O/R Designer Validation failed - during clean?

This problem appeared after I copied a property in a table. For some reason the copied property had the same storage name. Deleting this storage attribute in dbml xml for those copied properties solved the issue.

So the source of this problem is most likely some error in the dbml file. If you have version control, check what you changed and maybe you'll spot the error.

I had to close Visual Studio and reopen it. Solved this for me. In another case I had to roll back my DBML file, then close Visual Studio, and reopen it.

Looks like a bug for Microsoft to fix.

I had also the same problem, but the following procedure let VS always compile the code correctly:

Close VS

delete all files in the obj\x86 (and eventually x64)\Debug (and Release)\ directory

Then start VS again via command line using

<Path>\devenv.exe /ResetSkipPkgs (optionally: <Name>.sln to open directly the correct project)

(Not sure whether the /ResetSkipPkgs is necessary, but another article told so. I made a small batch script which does all of this automatically). The code should compile now without any problems!

For reference, my script file looks like this:

del /Q C:\[...]\[...]\obj\x86\Debug\*.*

"C:\Programme (x86)\Microsoft Visual Studio 11.0\Common7\IDE\devenv.exe" /ResetSkipPkgs C:\[...]\[...]\<Name>.sln

(I always develop in debug mode, thus I only delete the matching x86\Debug directory...)

vs2010 was giving me this error while vs2017 was building it fine, running vs2010 with /ResetSkipPkgs (Andre's answer) solved for me.