SAP Note 27130 - A grouping cannot be defined in the layout

Symptom:

A new grouping can be created when maintaining the layout for a partial screen. It is in fact possible to specify a name and a text. However if you are on "Grouping definition" level and try to create entries using "New entries", the error message "Select one entry only as a heading" is issued.

Cause and prerequisites

At least one of the entries must be selected as a heading. The check continues to be made even if no entries exist.

Solution
Repair in SAPL0C29 (see below)