What's going on is that Illustrator is running out of RAM during the display/render process. When you place multiple high-resolution files into an Illustrator document, Illustrator uses RAM to render the objects etc.
- Illustrator is a 32 bit application is not taking advantage of your 6 Gig of RAM, but only accesses 3 gigs. Nothing you can do will make Illustrator use the rest.
- When you place so many files into illustrator, it attempts to render them, using up your RAM.
- Make sure you're LINKING files, not PLACING them on the actual page.
- Reduce linked file's sizes to exact dimensions you need. (Don't use a 20" x 20" 1200 dpi image if you're printing the file at 300dpi.)
- You can force Illustrator to display Document Raster Effects Settings to 72ppi, which will reduce some of the RAM requirements, until ready to output. Also turn of Anti-aliasing in the preferences while manipulating the document.
- Illustrator is not a page-layout application. Learn to use InDesign for page layout rather than Illustrator (I'm still working on this myself.)
- Once a file gives the dreaded FILE IS NOT READABLE error, you're basically stuck. Your only recourse is to close the application and open it again. If you save a file, which gives the error on opening, the file is pretty much useless. I've found no way of getting into a file that Illustrator has saved in an "unreadable" state.
Many thanks to Wade Zimmerman for help on these notes.