The solution will not allow debugging / building / cleaning after merging visual studio 2012

Question

When merging the two branches, the Visual Studio solution and the project files did not match, so they had to be merged manually. Now, when I try to create or clear a solution, I get the following message:
"The debugger cannot continue the process. The project file" "has been renamed or is no longer in the solution."
Is there a way (not brute force) to understand what is wrong with the files and fix it.
What does this error message mean?

The solution consists of 10 projects, 2 of which can be used as starting points for unit tests and for functional testing.
When I tried to take this file from one of the branches, there were many files missing from both sides.
Setting the right startup project does not help.

Answer 1

I found a solution in this thread
In short, one of the projects did not update the ID of its dependencies correctly, as a result of which he could not use them.
In addition, one moral from history does not allow your branches to disperse for more than a year.