Report group is being regenerated (change to library &)

What causes this issue?

The current report group is assigned to library &V1&. Changes were made
to the library, so that the report group has to be regenerated (such as
a change to the order of characteristics).

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?

Error message extract from SAP system. Copyright SAP SE.