I removed all the custom functions that I put into functions.php - still happens.
Something interesting is that when I have Jetpack installed, the checkout page (after about 3 seconds) goes blank and all that is left is the smiley face in the upper left corner - which is jetpack's analytics image.
Here's everything I've tried so far, and none of it works:
1. turn off ajax (add to cart) in woocommerce
2. disable groups plugin
3. turn off guest checkout so users have to log in to buy
4. Remove custom functions in functions.php
5. deactivate woocommerce and reactivate
6. Clear transient data (woocommerce > settings)
7. Remove ecommerce event tracking code (woocommerce > settings > integration)
8. Uninstall woocommerce (delete plugin files) and reinstall from a fresh download
None of this worked. I tried loggin in as a "subscriber" and it still breaks. The only time it all works is when an ADMIN is logged in. I'm stuck at this point.