Upgrade to 6100 causes 502 error rendering site unusable

Upgrade to 6100 causes 502 error rendering site unusable

I installed the service pack after coming back from vacation because I noticed it had some security bug fixes. I patched from 6013 to 6100. After applying the service pack 6100 the site no longer worked and provided us with a 502 error. I had to revert to a VM snapshot to get back up and running.