B4J Question Generating exe from jar with Jar2Exe

I want to distribute a B4J application both for Windows and Mac.
To simplify the user action, I have created an exe with Jar2Exe and it works on Windows.
I have tried to do the same for Mac and it doesn't work. I'm testing it on an old MacBook with OS X 10.5.8.
What can be the problem?
Thanks Erel. But there seems to be another issue, Jar2Exe can generate the right file.
I have tested the jar file and it doesn't work either. (the same jar file works on Windows).
I have read that the Java runtime in MacOS was supported by Apple until OS version 1.6.-- and from 1.7.-- it is provided by Oracle.
As my Mac has OS version 1.6.8, I can't update java runtime. My question is:
What is the minimun java runtime version required to run the code generated with B4J?