what is the system info of your computer? RAM, processor, etc?
Intel (R) Core (TM)2 CPU
6400 @ 2.13GHz
2.13GHz. 0.99 GB of RAM
90% free resources
It's been my experience that with computers that only barely meet the system requirements across the board for Flash or many other Adobe products tend to crash those products even when performing the most seemingly mundane tasks. If installing more RAM is not an option, try keeping all other programs/windows closed while working in Flash. (http://www.adobe.com/products/flash/systemreqs/)
One little trick that I have found to be usefull on slower machines is to not Import to Library, but rather Import to Stage. Importing to the library also adds the step of creating a graphic symbol (CS3) or a movie clip (CS4), whereas Importing to the stage does not.
Also, are you pulling the images off of an external device like a USB drive or an external hard drive? This could be another - and probably the real - reason you are experiencing the error. Try putting the images on your HD, then importing.
You may still want to get some more RAM to handle Flash CS4.