For Chrome/Comodo Dragon/Ironweb: https://chrome.google.com/webstore/detail/edit-this-cookie/fngmhnnpilhplaeedifhccceomclgfbg
In Chrome after installed add-on just click new cookie icon next to address bar while you are in forum main site, then click "Remove all" and refresh website, re-login and see if 400 error "Bad request" or 404 "not found" still exist.
For Firefox should be similiar thing, I don't use it.
Don't know if Maxthon and Opera have addons like this, if so post your finding
Hope this helps, worked for me as I had every thread I open error 400.
Quit at Cerberus 2 event, returned before Stormfront.