Requisition ends up Forarded/Pending instead of getting Certified

We have had a number of cases where Requisitions were created and approved but then get Forwarded and end up in Pending status instead of getting Certified.  The users then must get someone to go into the Workflow and retry the process because pulling the Requisition back and resubmitting it also results in the Requisition getting Approved but being set to Pending and not Certified.  In each of these cases, the person doing the Certification is the same (but that person can usually certify with no problem), so we are wondering if there is some kind of setup issue that might be causing this to happen.  We are still using 11i (11.5.10.2).