Disclaimer: What follows is not the recommended guidance from patterns & practices, rather it is my own personal "last resort" technique. I wasn't originally planning on posting this, however after just helping a customer who was experiencing the same issue (yes you Travis), I changed my mind.
Here's a horror story. A few weeks ago, I had to deliver an internal talk to a group of Architect Evangelists on WCSF vNext. At around 9:30 PM the night before, I realized that I needed to have the latest version of our WCSF Guidance Package installed in order to demo the new recipes. And so, I downloaded and 'attempted' to install the latest GP. During the install I received a nice friendly message from the installer that I needed to upgrade to the latest version of GAT/GAX 1.3. On first reading this I had an "uh oh" moment and felt a big lump in my throat. I've been down the uninstall GAT/GAX routine before and it's NOT pretty. Let's just say, my premonition was correct. So over the next four hours I unsuccessfully tried many combinations of each of the following steps.
With each attempt, I came up empty. Searching online through blog post after blog post, forums, etc also yielded very little other than a few mirages of false optimism. Part of my problem is that I did not have the original MSIs on my machine and was having a heck of a time tracking them down. Finally when I was literally at my wits end and thinking about how beautiful it would be to see my laptop flying off of a tall building, I hit gold as I happened on the "Windows Install Clean up Utility".
1. Download the utility and install it.
2. Execute it from the start menu. You will find it under Start->Programs-> Windows Install Clean up.
3. You'll see a list of all the programs installed on your machine. Select the ones you want to whack.
4. Click your heels together and say "GAT/GAX be gone! Factories be gone!"
5. Click the 'Remove' button.
6. Problem solved. (well sort of). This will leave residual entries in the registry, and files on disk which you'll need to go track down and clean up yourself.
This little beauty saved the day! After 4 hours of banging my head against the wall, it look less than 5 minutes with this utility to whack any remnant of GAT/GAX, SFT and any custom GPs. 10 mins later, I had all the new installations including the newer GP. 2:30 am, Aaah sleep at last.