Every couple of days, MSN keeps telling Mail that I need to input my password. I don't know why this started occurring, it started just a week ago. Would this be because I linked my Windows 7 laptop account with my Windows Live ID? This is driving me up a freakin' wall everytime I turn on the screen and log in to find that Mail is requesting a password for my MSN account.
Check your KEYCHAIN file and the Keychain for this account. It could be corrupted. You can try deleting it and then re-inputting the login info and create a new keychain item for this account. I have seen this on some of my machines from time to time. Also, see if you can change the account prefs on the MS website to keep your account ALIVE longer.