It seems that Steinberg are not coming clean about a major REWIRE bug that is affecting both mac and PC users.
Judging from the amount of posts about this (with few definitive solutions).
I recently upgraded to a mac pro intel quad-core. I then bought the cubase 6.5 upgrade and installed it.
I also installed my copy of REASON 3.5 which is 32 bit and mac/intel compatible - it runs fine.
However, rewire just does not work - it doesn’t even show. I have tried all the fixes that I have seen posted, the main one being that both should be running in 32bit mode. I have even uninstalled and re-installed both programs.
PROPELLERHEADS tech support’s answer was “make sure both are running in 32bit mode”.
Although it has been more then 48 hours (5 days) since I sent my support request to Steinberg, they have still to answer. I recently learned that Propellerheads and Steinberg developed REWIRE together.
I don’t know how much Steinberg monitor forum posts, but I’m hoping that they will soon post an announcement acknowledging this bug and more importantly A FIX 
It’s true, in the Cubase 6.5, there is 32-bit ReWire only. So, you hae to run both of applications in the 32-bit mode.
I have no probelm with ReWire on my Mac OS X 10.7 with Cubase 6.5, and other apps (Ableton Live, Sibelius, MAX/MSP). So, I suppose, this is not majore ReWire bug.
Can you try to Repair Disk Permission from the Disk Utilities? Just to be sure, your permission is OK.