Keep getting logged out !!

Hi I am having problems with using the administration page on my forum, I am logged in as admin but every time I select a title to go into I get kicked back to the log in screen, I am using firefox, and I have cleared my cache numerous times but this does not solve it, sometimes it is ok, but more often than not, I log in, go down to the bottom of my site and select administration, select a title selection and heypresto I am back at the admin log in page again. This is getting rather tiresome and annoying, this has only been happening over the last two days, I haven't installed anything new either.

My site is http://www.derehammcc.net/index.htm

Please can you discover what is occuring, thank you

Try another browser? See if the problem persists?

It doesn't happen with internet explorer, strange? It never happened before, as I prefer firefox and don't realy want to start using a different browser. So it is either a browser issue or a coding issue I can only guess?

Try to clear your cache and see if that helps.

http://help.forumotion.com/frequently-asked-questions-f5/how-to-clear-the-cache-in-firefox-internet-explore-chrome-t22597.htm

Done that, doesn't make a difference!

Try this http://help.forumotion.com/frequently-asked-questions-f5/log-in-problems-t45.htm