Dawa,
Is there anywhere in your application that the table Stafile is open exclusive? May be one user attempt to insert a record therefore other is open that table exlusive, doing some REINDEX or PACK...
By the way according to help the right sintax of RLOCK is:

RLOCK([nWorkArea | cTableAlias] | [cRecordNumberList, nWorkArea
 | cTableAlias])

so you must change

 if rlock("0",'stafile')

to

 if rlock('stafile')

In addition, You can put a messagebox before ROLLBACK to annonce to user that no changes is commited.