I was getting same error while i was using TFS for source control, but when was updation file ouside visual studio then at the time of check in i was getting "Unable to perform the get operation because the file already exists locally. All of the changes were either unmodified files or locks. The changes have been undone by the server. And A non version controlled file or writable file by the same name is already existis.
Solution: I tried many short tricks to solved this problem like installation of power tools but not worked for me. Then i backup-ed all my files and got latest version of file from source control and then checked out for edit. Now i replaced all my backup-ed file to back and tried to checked in again.
Its worked perfectly without any problem.