[F] phpBB2 convert Guests?

[Rovin]

I have just converted from phpBB2 and on the Board Index in the Last Post column, I get:

In X
Today XX:XX PM
by Guest

But when I view the post, the Guest isn't a Guest - if you see what I mean. How can I fix this? I have tried Recount/Maintenance.

MyBB 1.2.12

Thanks a lot.
-Rovin