Generate report group & first

What causes this issue?

To execute reports included in a report group, you must first generate
the report group. The report group you have selected does exist, but
has either not yet been generated or not generated completely, and
cannot therefore be executed.

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?

Generate the report group before you select, output, or vary.

Error message extract from SAP system. Copyright SAP SE.