ANDREA FERRANDI The purpose of version 1.3.6 was exactly to remove any problems with MacOSX.
Now you can use it with Java 5 (matrex_1_3_6_macosx_32.jar) and Java 6 (matrex_1_3_6_macosx_64.jar) as you can read in http://matrexblog.blogspot.com/2009/06/matrex-136.html .
Please report a bug if there are still problems.
(Version 1.3.6)