If you are unable to login, please check the following :
Make sure you are entering the correct email address, exactly as it appears in your account ( including any capital letters etc )
Make sure your password is correct. Alternatively, use the password reset feature.
Troubleshooting
Check that your browser supports cookies.
Check that your browser supports Java and its enabled
If you are repeatedly unable to login, please close your browser and clear / refresh your cookies and browser cache.
For full details on browsers, cookies and cache, and instructions to clear / refresh your device, please see : Browser Guide - Clearing Cookies / Cache / History