Just another CPU, -6101 error...

[Seraplane]

And I can tell you right now, my CPU is not the problem. I just checked it and it's not using over 45% while playing back the recording. I have six audio tracks with audio recorded on them, five of which have a 7-band EQ plug-in and all of which have the Compressor/Limiter Dyn 3 plug-in on them. I have four MIDI tracks, three with Minigrand plug-in and one with XPand2 running an organ sound. The project runs without the error message, and quite smoothly, if I make all of the MIDI inactive. If I make the MIDI active, it works fine til it comes to a part of the song where two MIDI tracks are playing at the same time, then I often get the error 6101 saying I'm out of CPU.

I have been adjusting settings on my Mac lately, so I'm hoping I didn't cause this. I assume it's just a Pro Tools thing. I've recently been addressing some latency issues. My Playback Engine has no Delay Compensation set on it, but I did check the box for "Minimize Additional I/O Latency." I've got my CPU usage limit bumped up to 90% (lot of good that does) and I even have the box that says to ignore error messages during playback checked (also, lot of good that does). I bumped my sample rate up to 1024, too. I'm not really sure what to tell you, so I'm just giving you as much information as possible. Also, whenever I hit "Ok" on the Playback Engine Window, I get a pop-up saying that the current playback engine does not support a sample rate of 44.1 kHz. Not sure what that is about. I'm using 44.1 kHz and it still runs after I exit out of that.

Edit: Running it on Macbook Pro 2.4 GHz Intel Core 2 Duo, 4 GB 1067 MHz DDR3, Mac OS X Version 10.6.6, Pro Tools 9.0.1, interface is Presonus Firestudio Project.

The errors have become so frequent that it makes it impossible to record. Please help.