Touchdown and Outlook sync problems
I was having this same trouble (and the Touchdown manual is NO help). After "googling" around a bit, I discovered that you need to make sure that there are no events, contacts or tasks that still carry the category you are trying to get rid of. If there is even one task in the past with that category, Touchdown will still show that category, even if the category has been deleted in Outlook. Once I tracked those down and changed the category to something else, Touchdown synced correctly (except for one category that I still apparently have an event for somewhere in the distant past).