After further investigation, I have some more ideas.
Login as Host and select Host|Dashboard
1) What is the server time?
It may sound like a funny question, but I am quite serious. Is the server time the same as http://nist.time.gov/?
2) What is the ASP.NET identity?
Far fetched, but it may not have access to the certificate store. Highly unlikely as this was working before.
3) Was IIS reset after installing the chained certificates?
iHost restarted your website/apppool, but iisreset may be required. Just a stab in the dark.
4) Will iHost check the server security event log for information related to the event?
If the error is reproducible on demand,this should be an easy check.
5) Will iHost run this tool on their server?
http://www.iis.net/community/default....
This is a Hail Mary pass to help find the cause. I really doubt they would take a chance at this level of expertise.
At this point, I believe your only other option is to install your website and data on a completely separate server to prove if it works or not. I am even willing to offer a test DNN platform if you want to try this option.
Dwayne