The message "This program is not compatible with your Mac" may be shown when you try to start TaxCalc.
This behaviour will be seen if you are trying to run TaxCalc for the Mac on a version of OS-X that is not supported by TaxCalc.
TaxCalc needs OS-X 10.11 (El Capitan) or greater in order to run. It also requires a 64 bit Intel processor.
NOTE - Processors identified as Intel Core Solo or Intel Core Duo are not compatible as they cannot run the 64bit instruction set. Core 2 Duo processors and newer will work.
If in doubt check the About This Mac option from the apple log on the top left of your screen. This shows you the Processor and Software version.