[eluser]babai[/eluser]
There is a problem for Internet Explorer 8 - the first login works, but when you log out, and try to login again, it doesn't work.
A temporary work-around is if you clear your browser cookies, you will be able to login again. That's why it sometimes works, and sometimes not. Also, Firefox or Safari or Opera seem to work fine, but not IE.
How to solve the problem?