Local Event ERROR : oracle.apps.ap.payment

Hi;

Recently SYSADMIN has been receiving several email of this nature daily.  Can anyone advise the cause and how to resolve?

Event Error Name: WFE_DISPATCH_RULE_ERR
Event Error Message: 3825: Error '-6550 - ORA-06550: line 1, column 14:
PLS-00201: identifier 'AP_PAYMENT_EVENT_WF_PKG.RULE_FUNCTION' must be declared
ORA-06550: line 1, column 7:
PL/SQL: Statement ignored' encountered during execution of Rule function 'ap_payment_event_wf_pkg.rule_function' for event 'oracle.apps.ap.payment' with key '317711'.
Event Error Stack:
Wf_Event.dispatch_internal()