Occasionally, GuildPortal may need to recycle application services for a configuration change or a code push. This can sometimes end your authenticated session with the web server (effectively logging you out). However, GuildPortal is designed so that an authenticated user can be re-authenticated automatically, if you check the "save" checkbox next to your user name and password when you login. If you have done that, and it is still happening, here are some other things to check:
1) Make sure you have cookies enabled. Cookies are completely harmless, and can only store data for a web site, which can only be then retrieved by that same web site (by domain name).
2) Make sure your security settings aren't too high. Even if you have cookies enabled, your general security settings (such as the "Internet Zone" settings for IE) might be so high as to prevent cookies, which actually provides no additional real security whatsoever.
If that doesn't solve the problem, try logging in with a different browser, with "Save" checked and with cookies enabled. If the different browser does not exibit the same behavior as the old one (e.g., you do not get logged out with the new browser), then you know it was a setting with the first browser causing the problem.