Front office: Invalid reentry in step &1

What causes this issue?

A process step was called up a second time in the course of processing,
despite it being indicated with an attribute that prohibits renewed
processing.

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?

Check the Customizing settings for the front office.

Error message extract from SAP system. Copyright SAP SE.