Need help with a weird problem I can't fix

Hi All,

I have an application that accepts audio data every 20ms. I decode the data and write it to disk. The problem is that I am getting corrupt data when I include some lines of code. Below will explain what I mean. Ultimately what I want to do is decode both inbound and outbound streams and mix them before writing. The trouble is as soon as I try and decode the ourbound stream something gets screwed.
See comments below:

            byte[] InboundG729L1 = new byte[10], InboundG729L2 = new byte[10];
            byte[] OutboundG729L1 = new byte[10], OutboundG729L2 = new byte[10];
            short[] InboundDecodedG729L1 = new short[80], InboundDecodedG729L2 = new short[80];
            short[] OutboundDecodedG729L1 = new short[80], OutboundDecodedG729L2 = new short[80];
            short[] inbound = new short[160], outbound = new short[160];
            short result = 0;
            byte retval;

            //Copy both halves of the RTP data into seperate arrays
            Buffer.BlockCopy(inboundRTP.RTPPayload, 0, InboundG729L1, 0, 10);
            Buffer.BlockCopy(inboundRTP.RTPPayload, 10, InboundG729L2, 0, 10);
           
            Buffer.BlockCopy(outboundRTP.RTPPayload, 0, OutboundG729L1, 0, 10);
            Buffer.BlockCopy(outboundRTP.RTPPayload, 10, OutboundG729L2, 0, 10);
           
            //Decode first half of data
            IntPtr p = Global.decode(InboundG729L1);
            Marshal.Copy(p, InboundDecodedG729L1, 0, 80);
            Global.freemem(p);

            //Decode second half of data
            p = Global.decode(InboundG729L2);
            Marshal.Copy(p, InboundDecodedG729L2, 0, 80);
            Global.freemem(p);

//****** If I uncomment the following 3 lines the data comes out corrupted. It is fine as long as they remain commented
//****** As you can see the 3 lines shouldn;t have any effect on what I am writing to disk.
//****** Ultimately I want to use the decoded output from below to mix both streams together.
            //p = Global.decode(OutboundG729L1);
            //Marshal.Copy(p, OutboundDecodedG729L1, 0, 80);
            //Global.freemem(p);
           
            //Copy both arrays of decoded data into one array ready to write to disk
            Buffer.BlockCopy(InboundDecodedG729L1, 0, inbound, 0, InboundDecodedG729L1.Length * 2); //Multiply by 2 because it is a byte offset and we are dealing with 16bits
            Buffer.BlockCopy(InboundDecodedG729L2, 0, inbound, 160, InboundDecodedG729L2.Length * 2);

            for (int i = 0; i < 160; i++)
            {
                byte wByte = inbound[i];
                bw.Write(wByte);
            }
}

The decode function is declared as

[DllImport("decoder.dll", CallingConvention = CallingConvention.StdCall)]
        public static extern IntPtr decode([MarshalAs(UnmanagedType.LPArray, SizeConst = 10)]byte[] bArray);

The function in c++ looks like

extern "C" __declspec(dllexport) short * __stdcall decode(unsigned char serial[L_FRAME_COMPRESSED])
{

      int bfi=0;
      short * retval = new short[80];
      
      va_g729a_decoder(serial, retval, bfi);
      
      return retval;
}

Any help on this one would be appreciated
Thanks,
Erik