I seem to be having the opposite problem of all the questions/solution I can find regarding "connect to Microsoft Exchange using HTTP". In my case I have a client (I'm an IT consultant) whose PC's/Laptop's Outlook client will "un-check" (randomly) the "connect to Microsoft Exchange using HTTP" option. They will then have to check it and then re-enter all the proxy settings.
The Exchange server is physically not onsite...it's at the parent company location so they need to have this checked to connect.
The PCs/Laptops have never been connected to a domain...there is no domain controller onsite at the location.
This issue started recently, I believe it was around November 2012. Prior to that it worked for years....the Exchange server is SBS 2003.
Your help is greatly appreciated.