Cannot delete TIB file

I have a number of Acronis full backups that are stored on a server as tib files. They are not disk image type backups, but rather file level backups of information that is no longer required. I tried to delete them from within Acronis but it says "Failed to delete backup archive... the archive is locked by another process or user". I stopped all services related to Acronis, but some process still has control of it. I tried a third party file unlocker tool but it says the file is not locked. Tried deleting it from a command prompt but that didn't work either. I uninstalled Acronis completely, re-booted the machine and even that didn't help. Any idea what is locking the tib files and how to unlock them?

Thanks.