I've frequently gotten this error as well. It's not something that I can readily reproduce (I've tried), just seems random.
My setup is as follows:
iMac 2.4GHz, 4Gb RAM, 320Gb HDD, M-Audio MobilePre USB I/O, M-Audio MIDISport 1x1 Uno. All project files are stored on a 250GB Western Digital Firewire External Drive.
I have had this error both using the M-Audio I/O as well as the built in hardware.
I was running Leopard 10.5.1 but two days ago reverted my system to 10.4.11 - besides this issue I was having others, like Bluetooth hanging everytime I resumes the machine from Sleep. I have not seen the error since then, and I was in Logic for roughly 12 hours yesterday, so mayhaps this did it for me? Also, since the reversion to Tigger, I haven't seen the "Overload" error either, which I had on occasion......
Hope this is helpful to someone.