XP Screensaver looses password

We have a new computer running Windows XP Pro, with all of the updates.
When the password protected screensaver starts, the user cannot log back intohis computer. It thinks that the user has forgotten the password. However after maybe 10 to 15 tries the password may work, OR if the computer is restarted, then the password will work. Where can I look for a solution to this problem?

 

Is this a problem for all users or only one user? And if not for all users, what type of accounts have this problem, such as all the users but not the admin, one user and 1 admin, etc.