Not sure if you mean THIS site - but if you're getting logged out continuously, it means your cookie got corrupted. Delete it, reset it, you should be fine.

Delete any 'carnage.bungie.org' cookies in your browser.

Then visit the Profile Edit page:

http://carnage.bungie.org/haloforum/halo.forum.pl?profileedit

Put your password in three times (once for 'Password', twice more for 'New Password'), make sure you're saving the pass, and save the profile.

(Your profile has content in it - so copy that out before you start, so you can paste it in when you rebuild this.)

Once you do this, you should find that you're no longer being logged out regularly.

(If you meant some other site when you said 'this site'... I'm not sure I can help. :) )