HTTPS is working, but Certificate not trusted? Using Windows Server 2012 R2

I’ve been trying to get the free LetsEncrypt SSL certificate to work with IIS on Windows Server 2012 R2.

I went through the ACMESharp github tutorial ( and ) and got everything to work without errors on Powershell.

When I load the website in HTTPS, it works, but the browser complains about how it’s not completely trusted.

Please let me know if you have any ideas as to what’s going wrong. When I look at the Server Certificates in IIS, it looks good: Issued To (my domain), Issued By Let’s Encrypt Authority X1, Expires May 2016, Certificate Hash (redacted), Certificate Store (personal)

The URL I used when signing up for LetsEncrypt was:

Your site loads parts of the page (such as CSS, pictures, etc) over plain http. Such practice is called mixed content. You must load everything over a secure connection in order to eliminate this. There are ways to figure out what content that is, for example Security tab in Chrome Dev Tools.