I found 2 issues in 3.1.0-beta1-linux:
1. The ant task does not make the launch4j installation directory the current working directory. Because of this, it is unable to find ./bin/windres, ./bin/ld, ./win32api etc.
2. The folders in the tgz distribution should be rwxr-xr-x but are rwxr-x---. (BTW the owner/group could be improved as well).