You need to use it for more than two hours during the first 48 hours after creating it ... could that be the problem?
Either that or someone is playing a trick on you by changing your password (they may be somehow guessing your current one, or they found where you wrote it down...) Perhaps you have a trojan program on your computer that is allowing people to steal your password (although I have difficulty believing that someone would be so persistent in stealing a bunch of SC accounts)