You can approve those accounts manually.
Go to: ACP > Users > Prune / Move Users
Then use these settings:
Usergroup: Users Awaiting Email Confirmation
Has not logged on for x days: 0
Join Date is Before: Leave default
Posts is less than: 0
Order By: Username
Click find and then simply check the 'Move' option and select the group you want to move them to, I guess your registered users group.
I usually do this on my forum once a week or so... because it is known vB sometimes fails to delivers emails.