We have been tweaking the site a bit and this has given some people logging in errors. Sorry for that hassle- it is related to caching which speeds up the site big time.
To solve it - here a few things that may help.
1 - Close the browser window and Reload the browser session, or force reload it using the ctrl R on explorer, firefox or chrome in windows. (command R for mac I believe)
2 - Try a different browser
3 - Delete your cookies - here is a fab guide http://www.wikihow.com/Clear-Your-Browser%27s-Cookies
So sorry for this short term hassle. Normally cache errors go away after about 24 hours. If issues persist please post them in this thread below. Many thanks!