Hi Matt,
I guess you are using a deprecated plugin (qeupgradehelper), you need to take backup of the plugin. and remove the plugin from there location. And proceed the upgradation.
I hope it will work. But Please share the more details about your test site Upgradation. The version of your before upgradated site .
It will be better if you follow the Moodle Upgradation guideline and there scriipts only.
Regards,
Deependra