Unable to view/add users

I’ve been stuck at this for the past two days – I’ve tried googling and searching this forum multiple times but the previous threads either don’t match up entirely, or have fixes that don’t apply.

I have a fully updated WordPress install – initially MU – and am having issues with users in the main blog. I can add and view users for sub-blogs in network admin, but when it comes to blog 1 – there’s nothing.

All I see is this:
http://thepicardmaneuver.com/stash/problem.png

I recently exported everything from a sub-blog and imported it to the main site – but it refused to import the users. I tried to add them in bog 1’s admin – it said they had been added successfully. But still don’t display.

A lot of the fixes I found (one of them being handed out regularly) involved database fixes – but the fix didn’t apply and it’s only causing a problem with blog 1 and hasn’t effected any of the sub blogs.

Hopefully this makes sense – but if it does, can anyone give any advice?

Edit: for reference, I have tested this on the basic 2012 theme and disabled all the plugins as that’s usually the first thing people say hah, but… same issues.