This is a serious point...... elsewhere Freddie you said you were using 64 bit floating files as your recording preference.
I would imagine given the size of those wave files you'd need a fairly healthy I/O buffer set in Preferences-->Audio--->Sync & Caching===>Playback & recording.
Too small or large buffers there will cause dropouts while running under seemingly light loads. Basically Sonar can't get the data off the drives quick enough if too small or has to wait for the buffer to fill if too large. Result is a dropout either way.
HTH.