>Now we put code in RowDeleting (my colleague's attempts) and the RowDeleted event is never fired as well as this code doesn't seem to do the job. Can you help a bit here?

I don't think RowDeleted fires when you're manually using your own dataset instead of the SqlDataSource.

Calling Delete on the row just flags it for deletion. You have to call AcceptChanges() on the DataTable. Also, I wouldn't call Session.Clear() - you can just update the session var via: Session["dts"] = dts;

Session.Clear() blows away any other session variables which is usually a bad idea.

You may also really want to look into using parameters for your SQL update clause - viewstate can be hacked.