What causes this issue?

The freeze horizon is equal or longer than the planning horizon. This
will cause that no planning is done for the given product location as no
changes are allowed within the freeze horizon.

System Response

This error message is issued.

How to fix this error?

Check the planning horizon for the location product and/or review the
lead time for the external procurement relationships for that location
product. Adjust as per your business needs.

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.