Every once in a while I have this happen with other boards, and it is often due to issues with your browser (IE or Firefox). Flushing the Cache and Browsing History may help.

For Firefox, go to Tools/Clear Private Data. A new window pops up asking which items you want to clear. I leave Cookies and Passwords unchecked, and let it clear everything else.

For Internet Explorer it is Tools/Delete Browsing History. You want to clear Temporary Internet Files and History. Again I leave Cookies and Passwords alone.

Once you delete history you will need to enter each URL again to go to a site or select from your bookmarks. Once you visit a site the first time you can pull down the URL list and select it again from there.

Hope this helps!