Logic's Dreaded "disc Too Slow" Error Message! Options

[ryanie]

I am running a 1.25 Ghz G4 power book with 1.25 gig of ram. I am running Logic 6.4.1 and I constantly get the "disc too slow" error message if I use more than 5 tracks of audio and an audio instrument. I have tried buying more ram, freeing up space on my hard drive, freezing files, changing buffer size.. everythng! From what I can gather from other fourums it's a pretty common problem and it does not seem to be a hardware problem it seems to be a data transfer problem with Logic. My question is what can I do about it ????
Is it possible to upgrade my Logic 6.4.1 to a more later version of 6 (i dont want to buy logic 7) and will this even help matters?