Did you figure out where the problem is? I'm having the same issue with image sequences, even on cs6 and a mac. Would be good to get to know any workaraound.
This has always been an issue in Flash for a long time. Search the forum and you'll see. The best you can do is import in smaller batches (I'd recommend no more than 50 at a time).
Do you actually NEED to import a sequence of images? Any reason you're not using video?
FYI on a rig with 32GB RAM I can barely import 50 without needing to save to a new file, then import another 50. Also realize compressed size and actual size are different. If you want to see the actual memory footprint, open Photoshop, open an image and look at the bottom left where it tells you the actual memory required to display that image. For example a 39K JPG takes 225.0KB memory. A 360KB image takes 3.71MB RAM.
If your main reason to import the image sequence is publishing to swf, After Effects can also output to swf.