Oops...batch edit mistake. D'oh!!!
Using Jamroom
No quite sure what has gone on here but I can say that you were in the wrong place to delete comments. The Batch Edit is an 'advanced' tool that works directly on the datastores and it is possible to break thinks if used incorrectly. You cannot 'mass delete' comments with this tool.
What were you wanting to do? Just delete the comments on the group itself but keep its discussions?