First thing you can try is do a retry from workflow. If that is still failing, you can try running the stored procedure call that is shown in the error on a anonymous pl/sql block, using the listed values as parameters; check the stored procedure definition to account for parameters in/out and return types. This might help you on trying to pinpoint the error location within that program.
AP_WEB_EXPENSE_WF.SetStatusApproverAndDate, APEXP, 2869470, 318655, RUN
Thanks Amox...I did a retry on the expense and it worked.