I am aware of issues when running VZAM on the upcoming Mac OS Mountain Lion (10.8). Is a compatible version of VZAM in the works?
There is a 10.8 version of the VZAM on the vzam.net site. However, it is dependent on the device you are using.
If all else fails, restart the Mac in 32bit mode by holding down the 3 and 2 number keys while it restarts.