SAP Message AO609 - WBS element &1 has cost estimate - not possible to adopt plan values

Diagnosis
Costing was already entered in the Project Builder for WBS element &v1&
. It is not possible to adopt more plan values in this WBS element.

System Response
Action is terminated.

Procedure
Check if you want to keep the cost estimate on the WBS element. If not,then delete it. Once it is deleted, it is then possible to transferplan values from the appropriation request to the WBS element.