Domain Mapping crashing my site

This plug-in keeps crashing the backend of my site.

According to tech support at SiteGround the issue is that domain mapping is forcing https and I don't have an ssl certificate on that server - which is causing the error "Timeout waiting for output from CGI script"

I remember choosing the https option when I was choosing the settings for the plug-in, so I assume the fix is to simply un-choose that setting - however when the plugin is activated the backend of the site immediately becomes inaccessible, so I can't "unchoose" that option.