The ACME server was probably unable to reach http://XXXXX.XXXXX.XXX/.well-known/acme-challenge/eue_UrCJxw9Xpu3F7QxxIoXPq77GwaEuXSzj4RTj6so
Check in a browser to see if the answer file is being served correctly.
This could be caused by IIS not being setup to handle extensionless static files. Here's how to fix that:
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-win-simple.V1.9.1\web_config.xml