Unity3d crashes in batchmode from a null string

Howdy all, I've got an interesting one for you.

I'm working on creating an continuous integration / automated deployment server for our game using Hudson to manage the automation. The way it works is that we have an ant script that hudson will run every hour or so, tell unity to update the project through the asset server, and then start a batchmode build.

However, I'm not even getting that far. It turns out that if I try to launch Unity batchmode (without even doing anything else) from within Hudson, it immediately dies with:

[echo] Building Unity project.
[echo] /Applications/Unity/Unity.app/Contents/MacOS/Unity -batchmode -quit -projectPath /workspace/hudson/jobs/DailyBuild/workspace/project/ -executeMethod BuildEditor.Build
[exec] terminate called after throwing an instance of 'std::logic_error'
[exec]   what():  basic_string::_S_construct NULL not valid

Which, after a lot of researching I have come to find means that somebody tried to assign a null to a std::string, and which might have something to do with missing environment parameters that Unity assumes is there.

Every other attempt to isolate the problem by running Unity3d in batchmode succeeds, and calling the ant script directly from outside of hudson also succeeds.

I realize that what I have there might not be enough information straight up to diagnose the problem, so my first question is: what other information do I need to provide to help narrow things down? I'll start with the fact that I'm new to MacOSX, so I've already run afoul permissions problems and will probably do so again.

Thanks!

Details:

Unity Version: 3.30f4

Operating System: MacOSX 1.6.4

Hudson Version: 1.396

Tomcat: 7.0.8

Ant 1.7.1