Could not establish secure channel for SSL/TLS with authority

Hi Everyone,

An external provider is trying to submit files to an internal RHEL server via our TMG 2010 Reverse proxy.

I log a filter on the web listener IP address and can see it accepts the connect, but the external provider reports this error:

<ExceptionString>System.ServiceModel.Security.SecurityNegotiationException: Could not establish secure channel for SSL/TLS with authority 'fqdn.com'. ---> System.Net.WebException: The request was aborted: Could not create SSL/TLS secure channel.

regedt32 returns:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\Schannel\Protocols\SSL 2.0\Client]
"DisabledByDefault"=dword:00000001

Hope someone has seen this issue, thanks in advance.