In Intel, the program can be compiled for 32-bit (i386) and 64-bit (X86_64) versions. Perhaps your beta tester has an old Intel dashboard that only runs the 32-bit version of the OS, and you only compiled it for the 64-bit version. (on the contrary, OS is supported)
You can check the available architectures compiled into binary using the command file. i.e
% file Program.app/Contents/MacOS/Program
If you check this out on Dashboard.app, you will get the following output
% file /Applications/Dashboard.app/Contents/MacOS/Dashboard
/Applications/Dashboar…: Mach-O universal binary with 3 architectures
/Applications/Dashboar… (for architecture x86_64):Mach-O 64-bit executable x86_64
/Applications/Dashboar… (for architecture i386): Mach-O executable i386
/Applications/Dashboar… (for architecture ppc7400)Mach-O executable ppc
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