User locked out after first attempt!

I have the setting to lock users workstations after 3 failed attempts. However, I have 2 users who claim they are being locked out on the very first login attempt. For 1 particular user it happens the day after the password has changed (but she claims she used the correct password). The other user claims it happens every other week or so. Can you tell me why this is occurring to only these two users and not everybody else?
I know I could look in the security log (cause I have an audit on lock outs, but for some reason I am not able to view the security log even as administrator – ‘a required privilege is not held by client’).