Hey Art,
When I downloaded a new license file it was a .txt file. both the Mach4 and Darwin license I changed them to .dat file extension and put them in the license folder in Mach4. Then I checked Mach4 and it says it is licensed. But when I open the static gui it has a message in the history that says "Darwin license has failed with -33. I tried the latest Mach4 2067 and get the same result. I didn't uninstall the previous version of Mach4 and installed it over the other version so I will try that.
Dave