Had the same problem in OSX Lion.
I don't think RIM bothers to test anything, because this one should have been obvious the moment their QA ran the installer. Clearly no QA was done.
The problem is exactly what it says, so you need to overwrite the bogus binary with the one for Lion.
This command will fixed it (obviously change the path to your setup app if your not int he same directory):
cp /System/Library/Frameworks/JavaVM.framework/Resources/MacOS/JavaApplicationStub BlackBerry\ Java\ Plug-in\ Setup.app/Contents/MacOS/BlackBerry\ Java\ Plug-in\ Setup
