Issue in status change of Work item ID

Dear Eexperts,

When I am trying to change the status of work Item ID By using the FM : SAP_WAPI_WORKITEM_COMPLETE

Function module is giving error as ''LINE Work item 000006128155: Method SAP_WAPI_WORKITEM_COMPLETE not allowed for type F''.

Can anybody Suggest how to Change the status of work item ID ASAP.

Regards,

Ankamma.