Trouble with SSL and Domain Mapping

One of my multisites is having trouble with domain mapping; I'm hoping someone can help me problem solve it. The domain is validating (I see the green check mark) in the domain mapping admin screen, but when I visit the site I'm given a message that the security certificate can't be verified... It shouldn't be verified at all, as I'm mapping it to an http address, not an https address... but it keeps trying to go to https://sitename.com

I have other multisites set up without this problem occurring, and can't figure out what settings I must have set up differently... All of my multisites use https protocol, except if someone wants to map their own domain. Can you help me out?