There is a fix for this, taken from the ArcGIS Forums: 10.1 beta and comtypes. Edit comtypes module, under
PYTHONPATH\lib\site-packages and add the following entry to the
_ctype_to_vartype dictionary in
You may also need to delete
safearray.pyo in the same folder.
Also see page 5 of Mark Cederholm's 2012 Dev Summit presentation: ArcMap and Python: Closing the VBA Gap, and in the header of his updated snippets modules for 10.0, 10.1 and 10.2 respectively; index page: http://pierssen.com/arcgis10/python.htm
Alternatively, install comtypes with the above patch applied using pip:
pip install https://github.com/maphew/comtypes/archive/patch-1.zip
There is a pull request to merge the patch into master comtypes; still open because Enthought (rightly) won't apply patches without accompanying tests.