You may receive this error when Deployment Manager server or the web interface are starting up:

SocketException: No connection could be made because the target machine actively refused it 127.0.0.1:10300

The causes for this may be:

• The Deployment Manager service is not running. 
  To start the service manually:

1. 1. In the Start menu, type services.msc, and then click Services.
   2. In the Services dialog box, right-click the Red Gate Deployment Manager service, and then click Start:
      

• Some kind of anti-virus or other security software is preventing the connection.

• You have multiple IP addresses, and HTTP.SYS is only bound to one of them.
  This is a common configuration when you are using, for example, a Tomcat-based service (like TeamCity) and Deployment Manager on the same machine. You can check this via:

  netsh http show iplisten

  To solve it, either add 127.0.0.1 to the list of IP addresses HTTP.SYS can listen on using:

  netsh http add iplisten 127.0.0.1

  Or, in the registry under HKLM\Software\Red Gate\Deployment Manager, you can add the following string value:

  Deployment Manager.Raven.HostName = <host name or IP address to use>