I appreciate everyone taking the time explaining the problems you are encountering in regards to the login. It makes it easier to identify the problem.
In regards to using the BACK button, sometimes the page you're going back to comes out of your browser's cache (memory) rather than directly from our server. So if you weren't logged in on the previous page and you go back, most likely it was a local copy and not an updated version of the page. Either click on a link or CTRL-R or the F5 key will force your browser to get a new copy of the page.
In regards to the bookmarks, if you have bookmarked the homepage, it is possible your bookmark is causing problems. Your bookmark should either go to http://www.finescale.com/ or http://www.finescale.com/fsm/default.aspx or http://www.finescale.com/fsm/community/forum/ which will either take you to the homepage or the forum index. If your bookmark has a huge string of numbers and letters in it, then (unfortunately) your login will probably not work.
To change your bookmark on IE, click on Favorites. Locate your bookmark and instead of clicking on it, right click on it and select "Properties". The window that appears will have three tabs and you should be on the one labeled "Web Document". You'll see the URL field. If the url for the homepage is not one of the above then change it and hit the OK button.
Another post I made which Chris may be referring to (or has the same information) can be found here -
Techie Stuff: Browser Cache & Cookies.
Lastly, the login / authentication system restricts logins to a single computer (single browser). If you visit the forum at work and at home, you'll be forced to login each time you switch between the two. Here's something I had posted a long time before about this:
One thing I wanted to mention (although it doesn't sound like it's the problem) is if you use different computers you'll run into a situation similiar to this. The authentication process issues a "key" (which is stored in your cookie) that is verified every "x" minutes. If the key matches to the original, a new key is issued. If the key doesn't match, you're bumped out.
If you're using the same computer, it's not a problem. If you're switching between computers, everytime you login with one computer you're invalidating the key on the other computer.