During installation of the cloud enabled management internet gateway you are unable to add the Symantec Management Platform server to the list of servers.

Server certificate request failed.   The underlying connection was closed: An unexpected error occurred on a send

On the Symantec Management Platform the customer had disabled TLS 1.0and TLS 1.1.  They enabled the use of TLS 1.2 only by setting the registry key HKLM SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\tls 1.2\server\Enabled.

See following the article on Microsoft's web site located at: https://technet.microsoft.com/en-us/library/dn786418.aspx

On the internet gateway server we added the following registry key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v4.0.30319
"SchUseStrongCrypto"=dword:00000001

See https://technet.microsoft.com/en-us/library/security/2960358.aspx

See also KB 195561