PTR Systems hosts and manages a number of WordPress sites, and they run on a Windows Shared host at GoDaddy.
During the upgrade of one of the sites, the upgrade kept failing. Now as it’s a Windows host, the error message is an Error 500 Server error returned from IIS, not the PHP runtime. So this is pretty useless information.
GoDaddy has the functionality to install and overview your WordPress installations. Thankfully when you visit the overview of the failed installation it shows you error returned from the php runtime, and this information you can use to diagnose your problem!
In my case, the Jetpack plugin was causing the issue, so I simply deleted it from the plugins folder and the site is back up and running, but it states the upgrade has failed, at this point I simply re-installed the upgrade and it worked and then upgraded the remaining plugins.
So, I recommend in the future to make sure all your plugins are up to date, BEFORE you do the 4.4.1 upgrade in case one of your plugins is not fully compatible with 4.4.1. I believe the version of Jetpack I had installed was quite an old version, hence my upgrade issue. Hey, you live and learn!
Please note, the site I was upgrading is not live yet so it didn’t matter that it went down! All my other hosted sites are backed up and these major upgrades are performed on copies of the site then transferred over to reduce downtime, and these upgrades are performed in the early hours of the morning!