This only happens if you try to use the New Tracking Code (ga.js) (the new, and "improved" version) over the old Legacy Tracking Code (urchin.js). The bug's been around for a while, it's strange Google hasn't provided a clear fix for this yet ...
Update: new Analytics code doesn't have this problem anymore. If you edit your Site-details in Google Analytics, and view your Google Analytics code, you'll see something similar to this:
Error handling has prevented the error message to be shown. It is advised to use the code that Google provides, instead of the "hack" shown on top of this page.