Assessed values &1 and &2 overlap

What causes this issue?

The two time periods overlap. Overlapping of time periods is <ZH>not</>
allowed.

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?

Correct one of the time periods so that there is no more overlap.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.