SoapUI / Install4j crashes on installation on Mac 10.6

March 1, 2014
Failed to install SoapUI 4.6.4 on Mac OSX 10.6.8 by downloading the dmg.
This seems to be a problem with the install4j installer which crashes.
Double click on the installer (or right click then Open) will open a progress bar preparing the install4j installer. It gets almost to the end then silently dies.
Same problem is mentioned here: https://forum.soapui.org/viewtopic.php?f=13&t=22832

Messages in /var/log/syslog say
Mar  1 19:27:04 MM [0x0-0x1ce0cdf].com.install4j.5517-2803-0637-4585.10911[45636]: 2014-03-01 19:27:04.642 java[45671:903] *** NSInvocation: warning: object 0x1095b5390 of class 'ThreadUtilities' does not implement methodSignatureForSelector: -- trouble ahead
Mar  1 19:27:04 MM [0x0-0x1ce0cdf].com.install4j.5517-2803-0637-4585.10911[45636]: 2014-03-01 19:27:04.645 java[45671:903] *** NSInvocation: warning: object 0x1095b5390 of class 'ThreadUtilities' does not implement doesNotRecognizeSelector: -- abort
Mar  1 19:27:12 MM com.apple.launchd.peruser.501[269] ([0x0-0x1ce0cdf].com.install4j.5517-2803-0637-4585.10911[45636]): Exited with exit code: 5
Mar  1 19:35:19 MM [0x0-0x1cf1cf0].com.install4j.5517-2803-0637-4585.10911[46138]: 2014-03-01 19:35:19.056 java[46214:903] *** NSInvocation: warning: object 0x109628390 of class 'ThreadUtilities' does not implement methodSignatureForSelector: -- trouble ahead
Mar  1 19:35:19 MM [0x0-0x1cf1cf0].com.install4j.5517-2803-0637-4585.10911[46138]: 2014-03-01 19:35:19.058 java[46214:903] *** NSInvocation: warning: object 0x109628390 of class 'ThreadUtilities' does not implement doesNotRecognizeSelector: -- abort
Mar  1 19:35:37 MM com.apple.launchd.peruser.501[269] ([0x0-0x1cf1cf0].com.install4j.5517-2803-0637-4585.10911[46138]): Exited with exit code: 5