the most likely cause is reverse DNS contact your ISP
or do a tracert at http://www.network-tools.com/ if it does not show a reverse dns for your ip address then most likely this is the cause the other cause may be cookies or security settings.
check and make sure youare accepting cookies, and that your security settings are set to medium or medium low
I have lost access to websites that are considered secure and/or require a password (such as my bank website and fastmail account). I have checked my browser settings for security and privacy. I use mozilla primarily but also tried IE when I was unable to log on to such sites, but with no luck. I use winxp pro. I ran adaware the day before I noticed this problem. Any suggestions would be appreciated.