In the advanced section of the Primary Settings, you'll see where there custom cookie prefix is set. The only problem with changing this now is that it's probably going to cause problems with users that have been able to login, and they'll have to delete their cookies.
People that are having trouble logging in should just be able to use the "My Cookies" link down in the footer bar to delete them.
Rick,
I tought that if the user just use the My Cookies all will be fine, but it's not. I could not reproduce the problem here on my end, but I have a large population of users that are sending me e-mails complain that they could not login on the forum...
I understand that changing the cookies now would pose a problem for those users who ARE login in fine, so I'm kind on a corner here...