"An Empty File Name Is Not Valid" Compiling Android on Mac After Update

I recently updated my Mac (not my favourite development machine, let me tell you!) to the latest version of OSX, and discovered that it broke compiling for Android.

When I attempt to build an Android app now, it comes up with an ArgumentException, saying "An Empty File Name Is Not Valid".

Of course, the fact that it gives absolutely no details about what file it was looking for when the exception occured is a bit of an issue.

Note: Because this is an existing project, it's compiling in Unity 3, not Unity 4.

I've seen some other posts suggesting re-installing Java (done, no improvement).

Does anyone have any suggestions or advice? The upgrade may have seriously damaged my existing configuration, since I've had to re-enter all Wi-Fi passwords, which was rather unexpected.