PS on lopardo's post:: don't forget to close MSN Messenger completely first!
If you have Windows 9x with profiles enabled:
X:\WINDOWS\Profiles\<windows accountname>\Application Data\Microsoft
Addional tips (and "fine-tuning") on lopardo's post:
The thing that proberly solves it is not the registry editing, but the deletion of the MSN Messenger directory....
But be carefull in deleting it if you are not the only person using Messenger (or the computer): You don't have to delete the entire MSN Messenger directory, only the subdirectory for your "problem" account.
Under de directory "MSN Messenger" you'll see a bunch of numbers, these numbers represent different msn accounts. To find out the id of your own msn account, you can use
this utility from Choli. Once you've found the id number, delete only that directory
Cause and even further "fine-tuning" (to loose even less data):
If this fixed the error, then there was some screw up in your cache from MSN Messenger. Now, since your DP's, CE's and backgrounds are stored there it almost is certain that it has to relate to that....
* If you recently installed new emoticons with a emoinstaller, this could've been the source of the screw up....
* If you recently installed something that can change (or add) your DP's (like StuffPlug), and changed them, then this could've been the source of the screw up....
* Since there are not much (or non?) programs to deal with backgrounds, this isn't mostlikely the cause...
Now, with all this in mind, you can even further fine-tune the solution so that you will loose even less settings:
Only delete the directories (in your own MSN ID directory):
* "
UserTile" to reset and clear all your display pictures (if you changed or added a DP lately)....
* "
CustomEmoticons" to reset and clear all your custom emoticons (if you changed or added CE's lately)....
Don't delete both at once, but do it one by one and check if everything works in between (but don't forget to completely close msn messenger afterwards before you gonna delete the other directory!). Changes are greater in that way that you will only loose one or the other, but not everything!
/ 
