I tried to use the Fit to Fill effect in Avid Media Composer 6.5 and the message "The video effect could not rendered to the selected volume because it is locked or not available. Do you still wish to continue?" When I choose to continue, it says "Exception: DISK_LOCKED". I'm using a MacBook Pro Mountain Lion. Why is this message coming up and why can't I use the Fit to Fill effect? I'm also using a My Passport Studio 1 TB external harddrive FireWire 800.