Sorry for the late response. In the Preferences window, you need to be in "Advanced" mode (at the bottom). Audio->Sync and Caching has a Playback and Record I/O buffer near the bottom. These are the buffer sizes for reading/writing to a disk drive. I have these both set to 512 actually, and only bumped them up because of a General Error I got with a large project file. It was the only time I ever saw this error, and I never tried the solution that Craig mentioned above.