Optimized delta selection must not be activated

What causes this issue?

The system does not fulfill the prerequisites of the optimized delta
selection.
It has the following prerequisites:
Index 003 of table SWN_NOTIF exists
The conversion program RSWN_SET_APP_OBJ_KEY_HASH has run successfully.
The APP_OBJ_KEY_HASH column is filled for all lines of table SWN_NOTIF.
If these prerequisites are not met, you cannot activate the optimized
delta selection, because otherwise the UWL and Duet can no longer be
supplied with data (work items) and e-mail notifications can no longer
be sent.

System Response

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

How to fix this error?

For more information, see SAP Note 1526484.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.