This could be due to :

1. Your password is incorrect. We cannot remind you what your password should be, but if you wish to get a new password, simply click on the "Forgotten Password" link on the sign in page and try the new password you receive.

However it is more likely that :

2. You do not have "cookies" enabled in your internet browser. These are internet files that allow passage of information through the site. If you do not have cookies turned on, please follow the instructions here - http://www.google.com/cookies.html in order to turn them on, and then try to sign in again.

This is caused when you have not spent enough time on the page. The tracking system uses an algorithm to avoid “click-throughs” and any false page views. Please make sure you take the time to read the content on each page.