Getting calling sequence does not exist error for ap_holds_pkg.insert_single_hold

I am attempting to place a hold by calling ap_holds_pkg.insert_single_hold.  I am getting an error that reads, "APP-SQLAP-10000: ORA-02289: sequence does not exist occurred in AP_HOLDS_PKG.insert_single_hold <- with parameters(X_invoice_id = 7737951,x_hold_lookup_code = AMOUNT, X_hold_type =, X_hold_reason = ,X_held_by = ,) while performing the following operation: Insert into AP_HOLDS"

I was under the impression that it was acceptable to pass NULL as the calling sequence.  What sequence is it trying to locate?

Mike