Observed Behavior:
When I switch from any 32-bit version of Ableton Live to the 64-bit version of 8.4b1 (or vice versa), I am prompted to enter my password. If I cancel I see the error "You cancelled the authorization process. ReWire support was not installed. Restart Live to try again.". If I mistype the password I see the error "Authorization failed. ReWire support was not installed. Restart Live to try again.".
Workaround:
Not really unless you stay with either the 32-bit version or the 64-bit version.
Feedback:
Not needed, the problem is easily reproduced.
Status:
The problem should be fixed with 8.4b2.