SAP Message AA204 - External number allocation terminated - External number required

Diagnosis
External asset numbers are allocated in this class. A pop-up? window isused for this. You have terminated processing.

System Response
The system cannot create a master record without an asset number. Thesystem will display the initial request screen again.

Procedure
A. If you want to create an asset in this class, enter an asset number,
or
B. use an asset class which does not have external number allocation