Why does this SSL certificate validate fine in browsers, but not in .NET/Silverlight?

If I access https://www.mynetfone.com.au in a browser, the cerificate validates fine.

To do anything with this site in .NET, I have to override ServicePointManager and turn certificate validation off.

This becomes more of a problem with Windows Phone 7, where ther开发者_运维技巧e is no way to change certificate validation, and no way to remove certificates once you add them.

Is there anything obviously wrong with the certificate? What would the company have to do to fix it?

There are only a limited number of root certificate authorities with root certificates installed by default. For more details see "Windows Phone 7 Root Certificates_FINAL_121610.pdf" available from http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=8842

The other docs on that page also provide more information about SSL & certificates on the phone.