Corrupt files on Win 2k Server

We have a file server running Win 2k server. After a clean install of just the OS,updates and a back up program, ONE directory on a DIFFERENT drive corrupts. This has been an ongoing problem for an extended period of time. Have tried various backup programs, all with the same result – just one drive and a specific folder or files within it are corrupting. We have removed both drives and reformatted and still are encountering the corrupt file/folder issue. Have tried several back up programs – same results. The drive/folers/files are fine until you do a back up. After a back up the files are corrupt. Does anyone have a solution?, recommendation for a back up program that won’t cause this?, idea of why this is happening?