Error 12030 always occured when i upload the 2nd file

I upload files to a http server using Winet. But when the 2nd file was
uploading, i got the error ERROR_INTERNET_CONNECTION_ABORTED.

I upload a file by circle:

   uReaded = file.size(); // file size
   uCount = uReaded / MAX_BLOCK_BUFSIZE;
   uTail = uReaded  % MAX_BLOCK_BUFSIZE;

   inetBuffer.dwStructSize = sizeof( INTERNET_BUFFERS ); // Must be set or
error will occur
   inetBuffer.Next = NULL;
   inetBuffer.lpcszHeader = NULL;
   inetBuffer.dwHeadersLength = 0;
   inetBuffer.dwHeadersTotal = 0;
   inetBuffer.lpvBuffer = NULL;
   inetBuffer.dwBufferLength = 0;
   inetBuffer.dwBufferTotal = uReaded; // This is the only member used other
than dwStructSize
   inetBuffer.dwOffsetLow = 0;
   inetBuffer.dwOffsetHigh = 0;

   if (!pFile->SendRequestEx(&inetBuffer, NULL)) // pFile is a CHttpFile
type
    return RET_CODE_FAILED;

   for (int i = 0; i < uCount; ++i)
   {
    pFile->Write(pBak, MAX_BLOCK_BUFSIZE); // pBak is the begining of the
file
    OnFileUploadRun(MAX_BLOCK_BUFSIZE*(i+1), uReaded); // Notify others.
    pBak += MAX_BLOCK_BUFSIZE;
   }

   if (uTail > 0)
   {
    pFile->Write(&pBak, uTail);
    OnFileUploadRun(uReaded, uReaded);
   }

   if (pFile->EndRequest()) // end request.
    return RET_CODE_SUCCESS;


I found that when the 2nd file uploaded , an error throwed by MFC when
function pFile->Write(***) called. It costs me so many times; who can help
me.

Thanks very much.