Enter a cost element o r group

What causes this issue?

In cost center and order planning, you can either go into planning
using one cost element or a whole group of cost elements. However, you
cannot use both simultaneously.

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?

Please delete either the cost element or the group, or
Enter a value in one of the fields.

Error message extract from SAP system. Copyright SAP SE.