today I faced a problem with IIS and Certificates. The error was:
HRESULT: 0x80070520
I found a very good article here: http://blogs.msdn.com/b/kaushal/archive/2012/10/07/error-hresult-0x80070520-when-adding-ssl-binding-in-iis.aspx
In my specific case the problem was the permissions. I had to remove the certificate and set Administrators as Full Control to 'THIS FOLDER ONLY' and Everyone with Full Control over the entire folder.
After that imported the certificate again and it worked.
I am a bit worried with the Everyone permission, but this was the recommendation from this article: http://msdn.microsoft.com/en-us/library/ee248638%28v=vs.100%29.aspx
And, another problem solved!
