Test plan cannot be created

What causes this issue?

The system cannot generate a test plan since begin and end dates are
missing.

System Response

The system needs the designation date (or the planned designation date
in case designation date is not available yet) and the dedesignation
date (or the planned dedesignation date in case dedesignation date is
not available yet) in order to be able to create a test plan.
PS: if designation/dedesignation dates don't correspond to planned
designation/dedesignation date, the test plan is changed according to
designation/dedesignation date after designation/dedesignation.

How to fix this error?

Please enter planned designation date and planned dedesignation date

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.