我的autocad对象创建良好，但在acad.prompt()上收到错误。以下是错误：
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