vBulletin Installation/Integration Common Issues and Resolutions. Cookies and Login Problems!!
Your cookies are wrong or you did not install and correctly enter your vb
table prefix so the usergroups are not imported thats the only way your going to get invalid admin.
Try reinstalling after making sure your cookies in the forum are set like we note and pay attention to all the install questions making sure to enter any correct database info cookie prefix etc in vb