What does this traceback message mean?

[Robin Siebler]

I tried creating a COM object using win32com.client.dispatch and got
this error message:

Traceback (most recent call last):
  File "<interactive input>", line 1, in ?
  File "C:\Python22\Lib\site-packages\win32com\client\__init__.py",
line 92, in Dispatch
    dispatch, userName =
dynamic._GetGoodDispatchAndUserName(dispatch,userName,clsctx)
  File "C:\Python22\Lib\site-packages\win32com\client\dynamic.py",
line 81, in _GetGoodDispatchAndUserName
    return (_GetGoodDispatch(IDispatch, clsctx), userName)
  File "C:\Python22\Lib\site-packages\win32com\client\dynamic.py",
line 72, in _GetGoodDispatch
    IDispatch = pythoncom.CoCreateInstance(IDispatch, None, clsctx,
pythoncom.IID_IDispatch)
com_error: (-2147221005, 'Invalid class string', None, None)

Can anyone tell me what it means?