No error message on checkout. The file stays read-only and if I open SourceSafe, it shows that the file never got checked out.
Conversely, if I try to check a file in using SlickEdit, it goes through the motions of giving me a comment box but the file never gets checked in on SourceSafe's side and the file stays read-write. On SlickEdit's side, I get an error message saying "Cannot checkin the following files: [filename] These files may not be checked out, or archives may not exist for these files"
I didn't have "Act on projects recursively" turned on. I tried turning it on but it didn't work.