SAP Message AD391 - Output length for data type & is set to at least &

Diagnosis
Certain data types have a fixed minimum length. The output length iscomposed of the length of the data type and the formatting charactersrequired and, thus, also has a minimum value.
You have entered an output length that falls below the minimum outputlength for the data type you have selected.

Procedure
Use the minimum output length specified. You may need to check that youare using the correct data type. Press F4 or F1 on the field Datatype in the domain maintenance function to obtain an overview ofallowed data types or a brief description of the data types.