Hello,
I need some help. I would like to install a certificate. I am running windows Server 2012.
When it comes to the challenge / response it fails
Scanning IIS Site Bindings for Hosts
1: IIS autodiscover.thiry.net (%SystemDrive%\inetpub\wwwroot)
2: IIS exchange.thiry.net (%SystemDrive%\inetpub\wwwroot)
W: Generate a certificate via WebDav and install it manually.
F: Generate a certificate via FTP/ FTPS and install it manually.
M: Generate a certificate manually.
A: Get certificates for all hosts
Q: Quit
Choose from one of the menu options above: A
Authorizing Identifier autodiscover.thiry.net Using Challenge Type http-01
Writing challenge answer to C:\inetpub\wwwroot.well-known/acme-challenge/gJeek2ebWCb1n2bIqpN1Yp3-0-9cIDCnQ9Il34yYL0
Writing web.config to add extensionless mime type to C:\inetpub\wwwroot.well-known\acme-challenge\web.config
Answer should now be browsable at http://autodiscover.thiry.net/.well-known/acme-challenge/gJeek2ebWCb1n2bIqpN1Yp3-0-h9cIDCnQ9Il34yYL0
Submitting answer
Refreshing authorization
Refreshing authorization
Authorization Result: invalid
Authorization Failed invalid
The ACME server was probably unable to reach http://autodiscover.thiry.net/.well-known/acme-challenge/gJeek2ebWCb1n2bIqpN1Yp3-0-h9cIDCnQ9Il34yYL0
Check in a browser to see if the answer file is being served correctly.
Authorize failed: This could be caused by IIS not being setup to handle extensionless static files.Here’s how to fix tha
t:
1.In IIS manager goto Site/ Server->Handler Mappings->View Ordered List
2.Move the StaticFile mapping above the ExtensionlessUrlHandler mappings. (like this http://i.stack.imgur.com/nkvrL.png)
3.If you need to make changes to your web.config file, update the one at D:\LetsEncrypt\web_config.xml
But the page can be reached 
http://autodiscover.thiry.net/.well-known/acme-challenge/gJeek2ebWCb1n2bIqpN1Yp3-0-h9cIDCnQ9Il34yYL0
What I did wrong ?
Thanks in advance.
Laurent.
(maybe a more explicit message would had help)