Error during number assignment of group number &

What causes this issue?

An error has occurred in number assignment which cannot be specified
as the function module NUMBER_GET_NEXT has not responded with a return
code to the program which called it up.

System Response

The system cannot carry out the number assignment.

How to fix this error?

Please check your activities and notify your system administrator or
programmer if necessary.

Error message extract from SAP system. Copyright SAP SE.