Imported of SD card (or directory containing copy of SD card) stalls, virtually locking up the rest of the computer.

I have a Lumix camera with AVCHD videos and imported the whole SD card successfully several times but on a couple of occasions the import just stalls, virtually locking up the rest of the computer. I'm using Lion 10.7.5 and iPhoto 9.4.2.

I'm using a newly created iPhoto library and by about the 10th import this usually happens. The SD card is only 8GB so it's not a ridiculous amount of data.

I've tried using internal and external harddrive for the iPhoto library just in case there was some kind of hardware fault.

What I'm doing is possibly the first and most basic step any iPhoto user would do as soon they start working with iPhoto, and the fact that it fails on such a simple task is extremely concerning. The fact that it locks up the rest of the computer (ie. mouse still works but no other applications can be started) and I can't even click on the top-left Apple logo to select shutdown, is completely unacceptable.