"ORA-04062 signature of package has been changed

Problem:

Invoices->Entry,
enter a new invoice, getting:

FRM-40735: WHEN-VALIDATE-ITEM trigger raised unhandled exception ORA-04062
(Signature has been changed) 

Cause:

Some objects in database are not compiled properly.

Solution:

Please do:

1) use adadmin to
Compile the AP product procedures / packages.
Compile the AP libraries (pll)
Compile the AP forms (fmx)

2) retest the issue.