Planning level '&' marked for deletion

What causes this issue?

You are attempting to create a new planning level. However, this
planning level has already been marked for deletion during the current
session.

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?

Give the new planning level a different name.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.