When you log in, the system stores your userid and a hash of your password in a 'cookie'. Each time you visit a page here, your browser presents that cookie and the server verifies it to keep you logged in. If the browser stops sending the cookie (E.G because the cookie has been removed by a cache cleaner) then you will be treated as a guest by the server.
I've not had to log in here for months on several systems that I use regularly, so my suspicion is that something is wiping out these cookies - and your login info with them. You can check to see if these cookies are still present as follows:
IE on Vista/Windows 7
Browse to C:\Users\[username]\AppData\Local\Microsoft\Windows\Temporary Internet Files. Check for a file called something like [username]@army.txt. Mine for example is called bobbitt@army[1].txt, but shows up in Windows Explorer as cookie:bobbitt@army.ca/. If you can open the file (drag it into notepad) you should see about 9 lines with a variety of info here... DO NOT POST OR SHARE THIS INFO! If the file is empty or missing, you have no cookie, and will not be automatically logged in.
Firefox
In Firefox, go to Tools --> Options --> Privacy and click on the remove individual cookies link. This will open up a new window with all the cookies displayed. Type 'army.ca' in the search field and ensure there is one called SMFCookie10. This is your login information as described above. If it's not there, you won't be automatically logged in.
In a nutshell, this process will tell you if the cookies are being wiped out, or if they are still there. That should help us figure out what's going on.
Cheers
Mike