Hi there,
I am trying to add nested tabs in the CMS on a Class that is extending DataObject.

$SubjectTabSets = new TabSet(
            $name = 'SubjectAndCoursesPageTabSets',
            new Tab(
                $title = 'Qualification',
                $QualificationTabHeading
            ),
            new Tab(
                $title = "Study Journey",
                $StudyJourneyTabHeading
            )
        );

$TabbedContentTabSet = new Tab('TabbedContent', $SubjectTabSets);

        $rearrangeFields = new FieldList(new Tabset('Root',
                                $fields->findOrMakeTab('Root.Main'),
                                $TabbedContentTabSet));
        $fields = $rearrangeFields;

return $fields;

The above code keeps throwing the following error PHP Fatal error:  collateDataFields() I noticed that a field called 'SubjectQualificationTabHeading' appears twice in your form: 'Form_ItemEditForm'.  One is a 'TextField' and the other is a 'TextareaField'

Any ideas how to fix this. Basically the what I would like to achieve is the following
1. In the CMS, have a tab called "Individual tabs" on a class that extends DataObject
2. In the "Individual Tabs" have multiple tabs (may be 5 sub tabs) 
3. Each sub tab has form fields

Any help would be very helpful
Thanks
R