The report group has been changed (please regenerate)

What causes this issue?

The report group has changed since it was last generated. The current
definition and the generated Report Writer programs do not therefore
correspond with one another.

System Response

The Report Writer informs you of this situation each time you execute
the report.

How to fix this error?

In order to have the current report definition, generate the report
group. The generation is started either automatically when you start
the selection (if the "Generation not automatic" indicator is not set
for the report group), or manually using the Report Writer generation
function (<DS:TRAN.GR55>Execute report group</>).
Caution: during the generation, the existing data extracts for the
report group are deleted for technical reasons because the data
structure of the extracts is adjusted to the old generated programs.
If you still require the existing data extracts and it would cost you
too much time and trouble to recreate them, you should ignore this
message for the time being.

Error message extract from SAP system. Copyright SAP SE.