I'm using 1.0-RC1. I was not able to import pictures if too many pictures (ca. >50) where in the uploads directory. I had to import less pictures at a time.
This is an issue with your server/service. I upload thousands of pictures at a time but had to up 2 parameters in my php.ini file. I had to increase the max_execution_time memory_limit so that the process didn't time out. The loading process from a computer is a timeout issue. While the php is importing the server doesn't understand why it is taking so long and wants to stop the operation after a certain time. Upping these parameters will prevent it from stalling so to speak.