Execution indicators cannot be converted

What causes this issue?

You have started the program <ZH>RFBIEXFLAG</>, in order to set or
reverse the indicator 'in execution' for certain customers. However, no
customers exist for which the indicator can be changed.
This can have two causes:

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

All customers for whom the indicator 'in execution' is to be set, are
already in execution.
For the customers, for whom the indicator 'in execution' is to be
reversed, no open items exist that are in the execution. The reversing
of the indicator is nolt allowed then.

System Response

How to fix this error?

Error message extract from SAP system. Copyright SAP SE.