WBS element entered is not a grouping WBS element of type 1

What causes this issue?

The WBS element entered is not a grouping WBS element of category 1.
Only grouping WBS elements of category 1 (valid for all materials and
planning groups) have to be assigned to a plant so that the pegged
requirements display can be executed.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

System Response

Processing cannot continue.

How to fix this error?

Check your entries.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.