Error in user exit &1

What causes this issue?

An error has occurred in user exist &V1&.

System Response

INCLUDE ISU_VERARB OBJECT DOKU ID TX

How to fix this error?

Check the user exist.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.