the buffer of RTDX Host Library!!

Hi all, 
I'm Khoa, now I'm using Code Composer Studio v3.1 and C6713 board.
When I used RTDX to transfer data from PC host (MSVC++) to C6713 board, I
met this problem :
 PC host - MSVC++ : I used this command to write data :
            rtdx->WriteI1( Data_To_Send, &bufferstate )
but when I write 1025th byte,  the WriteI1 command cann't continuously
write (Failed result was returned) . At the moment, my C6713  received 1024
bytes.
I don't know why and I'd like to know How large the buffer of RTDX
Host Library should be.
I hope that you can help me to solve that problem.

Thank in advance,
Anh Khoa