Here is a quick trick. I was trying to check-in a few objects in a solution and encounter a strange error.
Could not find file 'C:\Users\Adminbefabcsd4\Documents\Visual Studio 2015\Projects\<MySolution>\<MyProject>\<MySolution>.btproj
Possible reason: If you are trying to check-in your object along with the solution file, you might get this error.
Possible solution: I cannot say it a permanent fix as I didn't find any technical reason for this, but below fix worked for me.
If you didn't make any changes in the solution itself, like adding/deleting a file, you should not include solution file in included changes. Remove solution file and check-in only object which you actually made changes.