SAP Message BP738 - No agent could be determined for the message to be sent

Diagnosis
Availability control is so configured that a message is sent to theresponsible person if an excessive funds commitment is entered.
The system could not find an Office user.

System Response
Availability control switches to the next action up - that is, itgenerates an error message instead of a warning and a Mail.

Procedure
Have a responsible person entered for the object with a budget.