Unfortunately I cannot remember what the error message was as it is currently on a test server that is unreachable (when I have access, sometime this morning, I will update this post with it). However the input should always be one of the four following:

SO_PC###.BIN
MS_PC###.BIN
SO_CV###.BIN
MS_MC###.BIN
[download]

The hashes represent unique identifier which are subject to change. So I need to search based on the first 5 chars as they are all BIN files.