I had real problems with error 1603 after a pretty big HDD problem, had corrupt sectors and lost a fair few important files. After some sifting through my error files - i noticed that MSN was crashing because of 'riched20.dll'
I suggest you go to windows/system32/ and rename riched20.dll to riched20.dll.old then try to reinstall msn, it worked for me
It seems that my old file got corrupt and wasn't letting msn work - it was also causing problems with other programs and reinstalling msn replaced the corrupt file and everything is working smooth now
(this was using XP by the way...)