Imported users not seeing the top Admin Bar


Please help me with this. We have just launched our new site yesterday and have noticed this issue, basically all the old users (which were imported via member import plugin) can't see the top admin bar.

I have tried reset the user role, even resign one of the user to be an admin, and that user still can't see the top admin bar. However, if I created a new user via either wordpress or the membership plugin, the new user can see the top admin bar no problem (with the same user role, subscriber)

The site is running a few WPMU plugins, including ultimate branding, membership and also running bbpress.

Thanks and Regards,