Diagnosis
When you deleted the mail data, an error occured:
a) when you deleted the MESSAGE object template during condition recordmaintenance.
b) when you deleted the MESSAGE object to be sent during outputprocessing.

Procedure
This error can have two reasons:
a) The object has been deleted in the meanwhile - no action is
necessary.
b) There is no basic problem with processing objects. If this
error often occurs, you should inform your system administrator.