C# Interop with WinInet

I have a C# FTP Class that connects to WININET through the PInoke Interop stuff.  When I use this to connect to a remote site and read a batch of files to save to my local machine the code will "freeze" on a call to InternetReadFile and FtpGetFile.  The file it freezes on is always random (sometimes it will get 10 files, sometimes it will get 20).  When I stop the program and restart it, it will pick up where it left off and freeze again 20 or 30 files down the line.  Here are the import tags:

        [DllImport("WININET.DLL", EntryPoint = "FtpGetFile", SetLastError = true)]
        private static extern bool FtpGetFile(IntPtr hFtpConn
            ,string strSource
            ,string strTarget
            ,bool bFailIfExists
            ,uint nFlagsAndAtrribute
            ,uint nFlags
            ,uint nContext);

        [DllImport("WININET.DLL", EntryPoint = "FtpOpenFile", SetLastError = true)]
        private static extern IntPtr FtpOpenFile(IntPtr hFtpConn
            ,string strFileName
            ,uint nAccess
            ,uint nFlags
            ,uint nContext);

        [DllImport("WININET.DLL", EntryPoint = "InternetReadFile", SetLastError=true)]
        private static extern bool InternetReadFile(IntPtr hFileFind
            ,byte[] pBuffer
            ,uint nBytesToRead
            ,ref uint nBytesRead);

And here is the implementation:

        public bool ReadRemoteFile(string strFileName, out string strBuffer)
        {
            bool bRetCode;
            IntPtr hFoundFile;
            uint nBytesRead = 0;
            byte[] arBuffer = new byte[MAX_BYTES_TO_READ];

            try
            {
                hFoundFile = FtpOpenFile(m_hFtpConnection, strFileName, GENERIC_READ, FTP_TRANSFER_TYPE_BINARY, 1);
                strBuffer = "";

                if (hFoundFile != IntPtr.Zero)
                {
                    bRetCode = true;
                    do
                    {
                        bRetCode = InternetReadFile(hFoundFile, arBuffer, MAX_BYTES_TO_READ, ref nBytesRead);

                        if (bRetCode && nBytesRead > 0)
                        {
                            strBuffer += Encoding.ASCII.GetString(arBuffer, 0, (int)nBytesRead);
                        }
                        else if (!bRetCode)
                        {
                            m_nLastErrorCode = Marshal.GetLastWin32Error();
                        }

                    }
                    while (nBytesRead > 0);
                    InternetCloseHandle(hFoundFile);
                }
                else
                {
                    bRetCode = false;
                }
            }
            catch (Exception ex)
            {
                bRetCode = false;
                throw ex;
            }

            return bRetCode;
        }

It freezes on the line:
bRetCode = InternetReadFile(hFoundFile, arBuffer, MAX_BYTES_TO_READ, ref nBytesRead);
       

I'm at my wits end and any help would be greatly appreciated.

Thanks