xemacs: Bad CPU type in executable
Running file on both executables will show you how the actual executable was compiled:

file /sw/bin/emacs


This will tell you why you're having issues running the file between different systems.

Obviously, with incompatible CPU types you'll face the error you're getting. 

Rosetta was available for 10.6, but not from 10.7 onwards. Could you have been using it somehow on an older machine?