The forums at
www.vbulletin.com/forum/ is a different username/password than the Customer Area at
https://www.vbulletin.com/customer/account/login/
You Customer Number isn't used on
www.vbulletin.com/forum/
It may be used to log in to th Customer Area:
https://www.vbulletin.com/customer/account/login/
Which are you trying to log into, the vbulletin.com forum or the customer area?