Xsocket Unrecognized Guid format

Question

I used xsockets for a while and i get following message very frequency.

System.FormatException: Unrecognized Guid format.
   at System.Guid.GuidResult.SetFailure(ParseFailureKind failure, String failureMessageID, Object failureMessageFormatArgument, String failureArgumentName, Exception innerException)
   at System.Guid.TryParseGuid(String g, GuidStyles flags, GuidResult& result)
   at System.Guid.Parse(String input)
   at XSockets.Protocol.XSocketProtocol.<>c__DisplayClass22.<Heartbeat>b__1f(Object o, ControlArgs args)
   at XSockets.Protocol.XSocketProtocol.<SetFrameHandler>b__b(IList`1 payload, FrameType op)

Is there any problem with those things?

update:

When i remove the following code, no exception is throw.

public override void OnOpened()
{
    this.ProtocolInstance.Heartbeat(notifyAction: (reason) => { Console.WriteLine("Heart beat :" +  reason); });
}