Okay
Couple things to check.
If you use vb3 integration you will be logged in as we use the vb3 cookies however if you cant login to admin it is because your cookies are not right thus you would need to check the settings table settings 181-183 and make sure they are set accordingly
If your not logged in at all using vb3 integration then I would suspect you have them installed on different domains.
as in one on
www.domain.com and one on domain.com
Some things to consider
If you have any problems you can post your urls here and I can tell you what the issue is.