Schannel 36888 - The following fatal alert was generated: 80. The internal error state is 301.

Apologies in advance if this is the wrong forum :)

We have a web application running under .net 4 which is erroring when trying to create an SSL/TLS connection to a remote site - server is 2008R2 with latest updates installed

We have been assured the certificates are correct and valid and I can telnet to the other IP on port 443, so it is not a network/connectivity issue, but when trying to establish the connection we get the following displayed.  The vendor has assured it is an issue with our server, but I am at a loss trying to troubleshoot:

   at System.Net.HttpWebRequest.EndGetRequestStream(IAsyncResult asyncResult, TransportContext& context)
   at System.Net.Http.HttpClientHandler.GetRequestStreamCallback(IAsyncResult ar)
   --- End of inner exception stack trace ---
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
   at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
   at System.Threading.Tasks.Task`1.get_Result()
   at xxx.SoapMessageSender.Send(Uri endpoint, X509CertificateclientCertificate)
   at xxx.Program.Main(String[] args)
---> (Inner Exception #0) System.Net.Http.HttpRequestException: An error occurred while sending the request. ---> System.Net.WebException: The request was aborted: Could not create SSL/TLS secure channel.

   at System.Net.HttpWebRequest.EndGetRequestStream(IAsyncResult asyncResult, TransportContext& context)
   at System.Net.Http.HttpClientHandler.GetRequestStreamCallback(IAsyncResult ar)
   --- End of inner exception stack trace ---<---

Schannel error 36888 is produced in the system event log with the following detail:

Log Name:      System
Source:        Schannel
Date:          17/06/2015 16:33:37
Event ID:      36888
Task Category: None
Level:         Error
Keywords:      
User:          SYSTEM
Computer:      servername
Description:
The following fatal alert was generated: 80. The internal error state is 301.
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Schannel" Guid="{1F678132-5938-4686-9FDC-C8FF68F15C85}" />
    <EventID>36888</EventID>
    <Version>0</Version>
    <Level>2</Level>
    <Task>0</Task>
    <Opcode>0</Opcode>
    <Keywords>0x8000000000000000</Keywords>
    <TimeCreated SystemTime="2015-06-17T15:33:37.177701300Z" />
    <EventRecordID>65182</EventRecordID>
    <Correlation />
    <Execution ProcessID="556" ThreadID="592" />
    <Channel>System</Channel>
    <Computer>servername</Computer>
    <Security UserID="S-1-5-18" />
  </System>
  <EventData>
    <Data Name="AlertDesc">80</Data>
    <Data Name="ErrorState">301</Data>
  </EventData>
</Event>

I have gone round in circles attempting to troubleshoot this - can anyone point me in the right direction please?

Thanks