Some antivirus programs quarantine .ff files as false positives. Add the Black Ops folder to your antivirus exclusions list.
If the registry key is missing or points to an incorrect drive letter (common after OS migration or drive reassignment), the executable defaults to the relative path. However, if launched from a shortcut with a mismatched "Start in" directory, the relative path fails. Exe-cannot-find-zone Black Ops Fix
This will require downloading 6-8GB of data. Some antivirus programs quarantine