[C.Birch]

check out the first post and this part:

Fix's

1) check your vBulletin cookies Prefix in vb's config file is set to bb like below:

// Prefix that all vBulletin cookies will have
// For example
$cookieprefix = 'bb';

if not set it to the above, if setting it to the above gives you errors with other hacks follow the steps on page 3 for editing messengers cookie call's.

this fix's the login error.

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note if you do have to edit that make sure you clean out your cookies and temp files before logging in to the forums again.