Others have the same issue, with the import button being grayed out. My trail copy expired, but I believe by poking around in the options and selecting another Aperture library and re-selecting, I was able to continue.
The problem is common enough, that hopefully Adobe will address. In the mean time, try repairing your Aperture library, checking permissions, exporting a subset of your library for a test, or try putting that library subset on an external drive. (Can usually avoid permissions issues.)
As a follow up I ended up making aperture libraries by cutting the big one in half (60,000 photos) and running each half. Then I cut the remaining one that wouldn't run in half and so on.... for four days. Finally I was able to narrow the problem down to, you're gonna love this, a Photoshop Elements file that had some how gotten into my Aperture library. It actually hung on its own file type.