Users attempts to delete a Group in Lists > Relationships > Groups and receives error: "This record cannot be deleted because it has dependent records".
Any Group which has been used to Bulk Merge operation or Marketing Campaign cannot be removed anymore.
Users may inactivate the respective Group by marking the Inactive checkbox on the Group record itself.
Note: Bulk Merge history is stored in Documents > Mail Merge > Merge History. Appropriate Group is displayed in Group column. Marketing Campaigns are saved under Lists > Marketing > Marketing Campaigns.