I recently requested support for a method of importing/assigning membership/subscriptions from a CSV import. David suggested I open a new thread to walk through issues encountered.
We are NOT using multi-site (at present but we plan to on the next iteration) but we are running BuddyPress.
First, the good news - we were able to create a basic php script to (successfully) import all 12,000 members with accurate subscription/membership options. If you'd like it, you can download it from here. Hopefully it'll grow up to be a plugin or membership option some day.
The only problem we've encountered (so far) is with site users with admin permissions not being able to add new users even if they have privileges to edit Membership settings or, if they didn't have membership edit privileges, being able to access the dashboard overall.
I've read through the installation instructions and don't see anything obvious that I've missed and searching the forum didn't bring anything specific up, so perhaps someone can explain what I'm missing there?