Message SAP WZ621 - Attachment &1 could not be added to the mail

Diagnosis
An attempt was made to create a mail message with attachments.Attachment &V1& could not be attached (business object SOFM,method Attach).
The error is probably in the task definition or the workflowdefinition, for example in the binding definition of the step inquestion.
INCLUDE NA_WF-ADMINISTRATOR OBJECT DOKU ID TX