BackToBackCall initialization failed

I'm facing with this error: "Invalid call states to establish BackToBackCall" it occurs on: "B2BCall = new BackToBackCall(inLegSettings, outLegSettings);"

Basically i have an application running on a TrustedApplicationPool server. The application accepts incoming call Browse a VoiceXml and if the user properly navigate the IVR the browser closed with exitcode = "1" which means that the caller must be connected to the user: "sip:opt01@intranet.local".

Here is my code:

public class BackToBackCallManager
    {
        public BackToBackCall B2BCall { get; private set; }

        public BackToBackCallManager(AudioVideoCall inboundCall, LocalEndpoint applicationEndPoint)
        {
            BackToBackCallSettings inLegSettings = GetInboundLegSettings(inboundCall);
            BackToBackCallSettings outLegSettings = GetOutBoundLegSettings(applicationEndPoint);

            B2BCall = new BackToBackCall(inLegSettings, outLegSettings);
            B2BCall.StateChanged += BackToBackCallManager_StateChanged;
        }

        private void BackToBackCallManager_StateChanged(object sender, BackToBackCallStateChangedEventArgs e)
        {
            CallManager.AppendLog(CallManager.LogPrefixName.BackToBackCall, "Previuos state: " + e.PreviousState +" New State: " + e.State);
        }

        public void Run()
        {
            B2BCall.BeginEstablish(null, null);
        }

        private BackToBackCallSettings GetInboundLegSettings(AudioVideoCall inboundCall)
        {
            BackToBackCallSettings retVal = new BackToBackCallSettings(inboundCall);

            return retVal;
        }

        private BackToBackCallSettings GetOutBoundLegSettings(LocalEndpoint localEndPoint)
        {
            BackToBackCallSettings retVal = null;

            ConversationSettings outConvSettings = new ConversationSettings();
            outConvSettings.Priority = ConversationPriority.Urgent;
            outConvSettings.Subject = "UCMA to group";

            Conversation conversation = new Conversation(localEndPoint, outConvSettings);

            AudioVideoCall newLeg = new AudioVideoCall(conversation);

            retVal = new BackToBackCallSettings(newLeg, "sip:opt01@intranet.local");

            return retVal;
        }

    }

Please note: inboundCall it's the AudioVideoCall started from caller to the App and it's State is: Established when BackToBackCallManager constructor was invoked. applicationEndPoint it's the localEndPoint established during application initialization.

I got totally stuck. Any ideas?