Remote Desktop Gateway client fails authentication with “Your user account is not authorized to access the RD Gateway”

Log Name:      Security
Source:        Microsoft-Windows-Security-Auditing
Date:          Date Time
Event ID:      6274
Task Category: Network Policy Server
Level:         Information
Keywords:      Audit Failure
User:          N/A
Computer:      RDG Server FQDN

Description:
Network Policy Server discarded the request for a user.

Contact the Network Policy Server administrator for more information.

User:
 Security ID:   NULL SID
 Account Name:   MYDOMAIN\USER
 Account Domain:   MYDOMAIN
 Fully Qualified Account Name: MYDOMAIN\USER

Client Machine:
 Security ID:   NULL SID
 Account Name:   Client machine's FQDN
 Fully Qualified Account Name: MYDOMAIN\WSDGBLND035$
 OS-Version:   -
 Called Station Identifier:  UserAuthType:PW
 Calling Station Identifier:  -

NAS:
 NAS IPv4 Address:  -
 NAS IPv6 Address:  -
 NAS Identifier:   -
 NAS Port-Type:   Virtual
 NAS Port:   -

RADIUS Client:
 Client Friendly Name:  -
 Client IP Address:   -

Authentication Details:
 Connection Request Policy Name: TS GATEWAY AUTHORIZATION POLICY
 Network Policy Name:  -
 Authentication Provider:  Windows
 Authentication Server:  NPS Server's FQDN
 Authentication Type:  Unauthenticated
 EAP Type:   -
 Account Session Identifier:  -
 Reason Code:   5
 Reason:    The Network Policy Server was unable to connect to a domain controller in the domain where the account is located. Because of this, authentication and authorization for the RADIUS request could not be performed.

Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Microsoft-Windows-Security-Auditing" Guid="{54849625-5478-4994-A5BA-3E3B0328C30D}" />
    <EventID>6274</EventID>
    <Version>0</Version>
    <Level>0</Level>
    <Task>12552</Task>
    <Opcode>0</Opcode>
    <Keywords>0x8010000000000000</Keywords>
    <TimeCreated SystemTime="YYYY-MM-DDTHH:MM:SS.739609200Z" />
    <EventRecordID>1463</EventRecordID>
    <Correlation />
    <Execution ProcessID="528" ThreadID="5748" />
    <Channel>Security</Channel>
    <Computer>RDG Server's FQDN</Computer>
    <Security />
  </System>
  <EventData>
    <Data Name="SubjectUserSid">S-1-0-0</Data>
    <Data Name="SubjectUserName">MYDOMAIN\USER</Data>
    <Data Name="SubjectDomainName">MYDOMAIN</Data>
    <Data Name="FullyQualifiedSubjectUserName">MYDOMAIN\USER</Data>
    <Data Name="SubjectMachineSID">S-1-0-0</Data>
    <Data Name="SubjectMachineName">WSDGBLND035.mydomain.internal</Data>
    <Data Name="FullyQualifiedSubjectMachineName">MYDOMAIN\WSDGBLND035$</Data>
    <Data Name="MachineInventory">-</Data>
    <Data Name="CalledStationID">UserAuthType:PW</Data>
    <Data Name="CallingStationID">-</Data>
    <Data Name="NASIPv4Address">-</Data>
    <Data Name="NASIPv6Address">-</Data>
    <Data Name="NASIdentifier">-</Data>
    <Data Name="NASPortType">Virtual</Data>
    <Data Name="NASPort">-</Data>
    <Data Name="ClientName">-</Data>
    <Data Name="ClientIPAddress">-</Data>
    <Data Name="ProxyPolicyName">TS GATEWAY AUTHORIZATION POLICY</Data>
    <Data Name="NetworkPolicyName">-</Data>
    <Data Name="AuthenticationProvider">Windows</Data>
    <Data Name="AuthenticationServer">RDSGBLND01.mydomain.internal</Data>
    <Data Name="AuthenticationType">Unauthenticated</Data>
    <Data Name="EAPType">-</Data>
    <Data Name="AccountSessionIdentifier">-</Data>
    <Data Name="ReasonCode">5</Data>
    <Data Name="Reason">The Network Policy Server was unable to connect to a domain controller in the domain where the account is located. Because of this, authentication and authorization for the RADIUS request could not be performed.</Data>
  </EventData>
</Event>

Log Name:      System
Source:        NPS
Date:          19/08/2009 12:39:56
Event ID:      4402
Task Category: None
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      RDG Server's FQDN

Description:
There is no domain controller available for domain MYDOMAIN.

Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="NPS" />
    <EventID Qualifiers="49152">4402</EventID>
    <Level>2</Level>
    <Task>0</Task>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2009-08-19T11:39:56.000000000Z" />
    <EventRecordID>1518</EventRecordID>
    <Channel>System</Channel>
    <Computer>RDG Server's FQDN</Computer>
    <Security />
  </System>
  <EventData>
    <Data>MYDOMAIN</Data>
  </EventData>
</Event>

Log Name:      Microsoft-Windows-TerminalServices-Gateway/Operational
Source:        Microsoft-Windows-TerminalServices-Gateway
Date:          19/08/2009 12:39:56
Event ID:      201
Task Category: (2)
Level:         Error
Keywords:      Audit Failure,(16777216)
User:          NETWORK SERVICE
Computer:      RDG Server's FQDN

Description:

The user "MYDOMAIN\USER", on client computer "X.X.X.X", did not meet connection authorization policy requirements and was therefore not authorized to access the RD Gateway server. The following authentication method was attempted: "NTLM". The following error occurred: "23003".

Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Microsoft-Windows-TerminalServices-Gateway" Guid="{4D5AE6A1-C7C8-4E6D-B840-4D8080B42E1B}" />
    <EventID>201</EventID>
    <Version>0</Version>
    <Level>2</Level>
    <Task>2</Task>
    <Opcode>30</Opcode>
    <Keywords>0x4010000001000000</Keywords>
    <TimeCreated SystemTime="YYYY-MM-DDTHH:MM:SS.739609200Z" />
    <EventRecordID>19</EventRecordID>
    <Correlation />
    <Execution ProcessID="4612" ThreadID="5296" />
    <Channel>Microsoft-Windows-TerminalServices-Gateway/Operational</Channel>
    <Computer>RDSGBLND01.MYDOMAIN.internal</Computer>
    <Security UserID="S-1-5-20" />
  </System>
  <UserData>
    <EventInfo xmlns="aag">
      <Username>MYDOMAIN\USER</Username>
      <IpAddress>192.168.0.189</IpAddress>
      <AuthType>NTLM</AuthType>
      <Resource>
      </Resource>
      <ErrorCode>23003</ErrorCode>
    </EventInfo>
  </UserData>
</Event>