Try turning off multi-processing, RAM preview, then clear your cache, turn MP back on and RAM preview. I've had some strangeness with the MP and sometimes previewing with it turned off fixes it.
Johnny Cuevas, Editor
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.