This fixed it for me.
I have this problem on an iMac with an external display using DisplayPort. Unplugging it doesn't let Netflix work, but deleting AirParrot did the trick.
It looks like someone used a quick and dirty method to detect screen grabbing software that could be used to record Netflix movies. Instead of allowing Netflix while they're not running, it simply blocks all HDCP playback if the software is even installed.
I don't see any mention of Netflix on the AirParrot site so it looks like we may be some of the first to figure this out. Please let me know if the fix works for you too.