Cookies
Sometimes, problems with browser cookies occur. To solve this take the following steps:

Internet Explorer: On the top of your (Internet Explorer) browser go to Tools -> Internet Options -> Delete Cookies. Then go to Delete Files in the same window, and after that click on settings under temporary internet files. Make sure that newer versions of stored pages are checked automatically. Then make sure the amount of disk space to be used for the files matches the amount of time you are on the web and how many sites you go to. 1192 MB should be enough. Then go to Tools -> Internet Options -> Privacy (on the top) -> move the solider so it shows medium or low. (Setting your security options to low may expose you to security threats, only try this as a last resort.)

Mozila: Tools -> Cookie Manager -> Manage Stored Cookies -> Remove all Cookies.

Firefox: Tools -> Internet Options -> Privacy (on your left) -> make sure the option for enabling cookies is selected (if not select it) -> clear -> OK.

MSN Explorer: More Choices (on the top) -> Settings -> (on your left) show all settings -> Change your cookie settings -> Change Now.