SAP Message SALERT050 - Send request for & has no recipients

Diagnosis
A send request was created for communication method &v1&. However,after the assignment of recipients, the send request has no recipients.
It may be that an attempt was made to assign only recipients that haveno communication data for communication method &v1&.

System Response
The send request will be deleted again.

Procedure
Ensure that all recipients have correct communication data.