Memory overload - happening out of nowhere

OK, running Logic 9 on a 2009 MacBook Pro, 8GB RAM, 64-bit mode. I'm a composer, so I have many multi-timbral instances open when I'm working. I realize off the bat that this is a lot to ask from my CPU, but the reason I am confused is that I've been working on one session for 3 weeks in this fashion, and have changed nothing. Before I created this most recent session I switched Logic from having run in 32-bit mode to now running in 64-bit. The session was working fine for me for 2 weeks. I have 2 omnisphere instruments with 8 channels each, and 2 kontakt instruments with 16 channels each. Almost all channels are being used. The only plug-ins I use (since I have a partner who does the mixing) are EQ's on each track with a high-pass filter, and an aux track running TrueVerb with each track bussed into it.

In the past week, when I open the session, all of a sudden I'm getting clicks and pops, and after a few seconds the playback stops with the error message "Error syncing audio and MIDI - sample rate 40262 recognized." Both Logic and my MOTU Traveler are set to 44.1, clock set to internal. Also, when I disable all the instruments and only run audio tracks that I've bounced, I'm still getting the system overload message. The CPU bar at the bottom is overloading constantly, whether there are 1 or 24 tracks being played.

I've tried switching back to 32-bit and running Kontakt in its own memory state, but to the same results.