Workflow shows active status but all activities are completed

 I have some workflows more than a year old that still show a status of active but all items under the activity history are completed.  When I try to cancel the workflow through the status monitor I receive the following message:

WF_PLSQL_ERROR (ERRNAME=WFENG_ITEM_PROCESS_ACTIVE) (ERRMESSAGE=3124: Process 'INVOICE_APPROVAL' for item 'BMCDBILL/IA [48730-15] 06-AUG-2009 15:59:47' is not active.) (ERRSTACK= Wf_Engine.AbortProcess(BMCDBILL, IA [48730-15] 06-AUG-2009 15:59:47, #FORCE))

What can I do to get rid of these workflows?  They have done what they were supposed to do and need to disappear.