title: Error when trying example Autocad usage
body: <p>My autocad object has created well but getting error on <code>acad.prompt()</code>. Following is the error:</p>
  
  <pre><code>acad.prompt("Hello")
  Hello
  Traceback (most recent call last):
  File "", line 1, in
  File "c:\users\snehal\appdata\local\temp\easy_install-lipjer\pyautocad-0.2.0-py2.7-win32.egg.tmp\pyautocad\api.py", line 162, in prompt
  File "c:\users\snehal\appdata\local\temp\easy_install-lipjer\pyautocad-0.2.0-py2.7-win32.egg.tmp\pyautocad\api.py", line 74, in doc
  File "c:\users\snehal\appdata\local\temp\easy_install-lipjer\pyautocad-0.2.0-py2.7-win32.egg.tmp\pyautocad\api.py", line 63, in app
  File "C:\Python27\lib\site-packages\comtypes-1.1.3-py2.7.egg\comtypes\client_init_.py", line 173, in GetActiveObject
  clsid = comtypes.GUID.from_progid(progid)
  File "C:\Python27\lib\site-packages\comtypes-1.1.3-py2.7.egg\comtypes\GUID.py", line 78, in from_progid
  _CLSIDFromProgID(unicode(progid), byref(inst))
  File "_ctypes/callproc.c", line 950, in GetResult
  WindowsError: [Error -2147221005] Invalid class string
  </code></pre>