If you are playing both Age II and Age I, perhaps you are being logged in via Facebook? That won't work on your Age I accounts because they are not linked with FB.

Other possible solutions:

Clear cache and cookies
Close and restart browser - if that doesn't help, shut down and restart pc.
Make sure you have all updates (browser, flash, java, windows, virus software, graphics card drivers, etc.)
Try a different browsers (Chrome, Firefox, etc.)

If you do (or did) all that and it still doesn't work, then it's beyond my knowledge.