SAP Note 15365 - CONVERT_NO_NUMBER

Symptom:

The payment print and tape generation program for POR (RFFOCH_U) terminates with CONVERT_NO_NUMBER.
Upon closer examination, you see that field REGUP-ESRRE contains non-numeric characters; this causes the error.

Cause and prerequisites

Account assignment errors with the POR reference number should really be trapped by a check routine in the invoice document. However, the customer did not activate that check in the country table, T005.

Solution
Menu path:
Tools -> Customizing -> Configuration menu -> Global settings Countries -> Field checks
Activate the check for Other checks, Other data.