This error may be triggered by two reasons: the associated budget line is included in a Pending BG document (BGA90 or BGA91) or the line was deactivated in a BG document with Event Type BG08.

The resolution is to work with your department accounting group to finalize the associated Pending BG document if there is one or process a new BG document with Event Type BG09 to reactivate the budge line if it was deactivated.