SAP Message AM756 - Number range interval & of object & is not internal

Diagnosis
The number range interval &1 for number range object &2 is notinternal.

System Response
Processing cannot continue as the program must get an internal numberfrom the number range interval &1 with the function moduleNUMBER_GET_NEXT.
The program is canceled.

Procedure
Call the transaction &3 to maintain the number range (or TransactionSNRO, Object &2, Go to -> Number ranges).
Delete the external number range interval &1.
It will then be created consistently as an internal interval at thenext call, and can be used to get the required internal numbers.