I also get the error: "Management Service is not installed on the web server. Please contact your system administrator."

I installed it under Windows Features/Roles -> IIS.

In the Internet Information Services (IIS) Manager, when clicking the servername, I have a section called: "Management", under that is "Management Service".

When clicking on "Management Service", I enabled/checked "Enable remote connections"  and made sure it is started.

It is configured for "Windows credentials only" and IP Address "All Unassigned", port 8172.

In SolidCP, under Servers -> Webserver -> IIS.  I gave it an ordinary URL (just pointing to the IP address of the server:  "http://some-hostname-to-ip".  The Service Port is default to 8172.  Windows Credentials is slected and No Netbios name is entered.