Since Flash Catalyst is designed for the screen, you should always use 72dpi. I find it odd that when you reduced the dpi from 300 to 72 that the file size did not change. It might be worth double checking the file again and making sure you are importing the right version.
If that still fails, your only option is to break the PSD into smaller portions. Look at the structure and see what you can isolate and/or merge. You might have some elements as editable elements for your design phase, but might actually be treated as a static element.
Hope this helps,
Thank you for the help!