I'm talking about the Testing server folder field. You must be talking about the URL prefix field. I've always had the URL prefix field set to webroot but the Testing server folder is set to the mapped network drive because that's all it will accept.
I've attached a screen-shot of where I'm at now, which is how I've always been prior to posting this thread. This is the only way it will work. Adding http:// or just using \\ in the Testing server folder field will not work.