Windows Messenger... Help!
 

This probably isn't the right place to ask, but it'd be great if someone can help me. I've also posted on the Microsoft public forum, but haven't heard any replies... This is driving me crazy...

Before and Background:
- Windows XP Professional (All but one DirectX update were installed from Windows Update)
- Windows Messenger 4.7.2009
- Norton's Antivirus and Personal Firewall 2003 (All patches and definitions are current)
- My contacts were grouped.

One morning when I logged on for the first time that day...
- Contact A (belonging to Group X, i.e., already on my list) asked to be added again. Contact A was using the same name as Contact B (belonging to Group Y, i.e., also on my list). I just thought it was a co-incidence, so I said OK. Contact A doesn't know Contact B.
- Then Contact B disappeared altogether.
- Contact A insists on being in Group Y (where Contact B used to be). I could move it into Group X, but that creates a duplicate entry (i.e., an entry will still be in Group Y). Now, there're 3 Contact A's in my list, 2 in Group Y, 1 in Group X.
- When Contact A's status changes, only one of these entries will change. This probably mean only one of these entries is 'real'...? If I delete the other 2, it'll delete all 3 or log me off the system.
- Every time I log onto Windows Messenger, Contact A (using Contact B's name) asks to be added.
- There seems to be a new group called 'Individual', which I can't delete. I thought the default unclassified group was 'Other People'...?

My brother also started to have this problem in the past week or so...

What's going on...?