Impex version issue? Install errors out after customer number entry

[BatCave]

I'm working on importing some members into a slightly older version of vBulletin (4.1.12)

I set up a development install of vB 4.1.12 and tested out the import process and got it all working fine.

However, when I installed ImpEx on the real forum site and run it, I just get the following error:

{"product":1,"version":"4.1.12","plugin_version":" 1.4.5"} and the rest is a blank screen.

I even turned 'impexdebug' to 'true' in the config and nothing changes. Same error. No clue what the error is from.

What does this mean? And more importantly, how can I fix it?