MacPOSx v2011 is not compatible with OS X 10.7 Lion
Do not Install Lion on your Mac if you are using MacPOSx v2011 or earlier.
MacPOSx runs on OS X 10.3 - 10.6 Intel and PPC Macs
MacPOS v2012 runs on OS X 10.5 - 10.7 Lion on Intel Macs only.
A new version of MacPOS, with a whole new look and features is due for general release very soon. Currently it is in beta testing.
We are also testing the various hardware drivers in OS X 10.7 and we will report on those after all of the testing is complete.
Please wait until everything has been tested to ensure 100% compatibility. OS X Lion most certainly will need an update before it too is a stable OS and all the bugs are worked out.