I found out a way to fix the sign in problems people are having (Windows XP). Exit MSN messenger 6 build 268, Goto control pannel > user accounts > *USERNAME* (Where username is, it is the current account you are working with in Windows XP, eg. admin) Top left hand corner click manage my network passwords. Delete the account you are having sign in problems with, and the passport.NET\* (Passport). Open msn messenger 6 again. Sign in and press remember my password. This will create a new passport entery, and fix the sign in problem. Worked for me.
