random exception

I have a segment of jawin code that pitches a COM exception about 33% of the
times I invoke it, but other times works fine?  It looks like this:

try {
  Ole32.CoInitialize();
  DispatchPtr web = new DispatchPtr("Marco2web.web");

  Object WebEncrypt = web.invoke("WebEncrypt", UserList);
  try{
     retString = String.valueOf(WebEncrypt);

  }catch(ClassCastException cce){
     System.out.println("Not a String: " + cce.getMessage());
  }

  Ole32.CoUninitialize();
  } catch (COMException e) {
    e.printStackTrace();
  }

All the documentation for Jawin assures me threading is no problem for dll
calls, so what else could be causing these generic and ultimately
meaningless COMExceptions whose detail message reads: "Exception occurred.\r\n"?