Current Plus! isn't fully compatible with MSNM 7.5. If you still wish to run MSNM 7.5 then disable customnames in Plus! preferences (plus > preferences > contactlist > custom names), as this is what causes most of the problems. If besides Plus! you are using Stuffplug NG make sure you get the beta for MSNM 7.5 (oversized DPs cause these problems) at
http://www.stuffplug.com wich is 95% compatible with MSNM 7.5 (only thing not working correctly is the ignore feature).
If you still wish to use customnames stick to MSNM 7.0.0816 till the new Plus! release at the 27th.
You did not have to update to MSNM 7.5 (it probably notified you about an update for 7.0, not necesarily meaning v. 7.5), you can still use MSNM 7.0.0816 if you wish (people with other OS'es than WinXP will have to aswell as 7.5 is only for Win XP). Just go to the MSN messenger site and change the OS (at the bottom of the page) after you click download. For WinXP choose the version for Win 2000
May i encourage you to use the search feature before posting, as this has already been answered many times before (almost every thread about MSN 7.5 is about the same thing), thank you.