Older versions of InstallBuilder will not work on OS X Leopard. If you need to support this version, you can download a preview of our upcoming 5.2.0 release
We are still working on fixing some issues. In particular, installers generated with this version will not work on Mac OS X 10.2. We know this version is considered 'ancient' but is still important to some of our customers, so we are currently looking at ways to address this. Please give the installers a try and let us know what you think.