Internet Explorer 6 won't allow 3rd party cookies to be set by default.
When the forum software tries to set the cookie when you login, IE6 blocks it unless you allow forumco.com to set a 3rd party cookie.
Fix it by doing either of two things.
Recommended: Stop using mallforum.com
Other solution: Ask all of your users using IE6 to do the following;
>> > Open Internet Explorer >> > >> > Click Tools > Internet Options > Privacy >> > >> > Under "Websites" at the bottom click "Edit" (on the right) >> > >> > Under "Address of Website" type forumco.com and click "allow". >> > >> > Click Ok. >> > >> > This brings you back to the privacy popup box. >> > >> > Click "Advanced" in the middle of the box. >> > >> > Make sure that "Overide automatic cookie handling" is checked. >> > >> > Under "first party cookies" check "Accept" >> > Under "third party cookies" check "Accept" >> > >> > Always allow session cookies should also be checked. >> > >> > click ok and ok again. >> > >> > Close all Internet Explorer windows. >> > >> > Open Internet explorer and try to login to the forum.