“_gat is not defined” Google Analytics ErrorMattias Geniar, Monday, August 25, 2008 - last modified: Wednesday, August 12, 2015
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.