CreateProcess Loop Problem (Visual C++ 2005)

When I call the method perform_single_upload() in this loop:

----------------------------
private: System::Void start_uploads(int i)
    {
        i = 0;
        while(i < master_list->Length)
        {
        //Create a single batch file containing the upload instructions
        create_single_upload(i);
        //Increment loading bar
        pb_Progress->Value::set(pb_Progress->Value::get() + 1);

        //Load and perform the batch file contents
        perform_single_upload();
        //Increment loading bar
        pb_Progress->Value::set(pb_Progress->Value::get() + 1);

        //Delete the batch file in preparation for the next one
        cleanup_upload();
        //Increment loading bar
        pb_Progress->Value::set(pb_Progress->Value::get() + 1);

        i++;
        }
    }
----------------------------

With perform_single_upload() doing the following:

----------------------------
        STARTUPINFO si;
        PROCESS_INFORMATION pi;
        LPTSTR szCmdline=_tcsdup(TEXT("upload.bat"));

        ZeroMemory( &si, sizeof(si) );
        si.cb = sizeof(si);
        ZeroMemory( &pi, sizeof(pi) );

        // Start the child process.
        if( !CreateProcess( NULL, // No module name (use command line)
            szCmdline, // Command line
            NULL, // Process handle not inheritable
            NULL, // Thread handle not inheritable
            FALSE, // Set handle inheritance to FALSE
            0, // No creation flags
            NULL, // Use parent's environment block
            NULL, // Use parent's starting directory
            &si, // Pointer to STARTUPINFO structure
            &pi ) // Pointer to PROCESS_INFORMATION structure
        )
        {
            //Something went wrong.
            AnError^ uploaderror = gcnew AnError();

            uploaderror->label1->Text::set("There was an error finding a batch
script file.");
            uploaderror->ShowDialog();
            return;
        }

        // Wait until child process exits.
        WaitForSingleObject(pi.hProcess, INFINITE);

        // Close process and thread handles.
        CloseHandle( pi.hProcess );
        CloseHandle( pi.hThread );
----------------------------

....my main process appears frozen until the loop in the first method
has gone through all of its iterations. I can't seem to figure out
why it doesn't update anything after calling the
perform_single_upload() method for the first time.

Is there any way to maintain control of my main application after a
CreateProcess(), or system(), or WinExec(), etc. call?