I propably found the error: According to /usr/lib/python2.5/_strptime.py, '%Z' is restricted to:[mirko@borg mercurial-crew]$ python -c 'import _strptime; print _strptime.TimeRE()["Z"]'
(?P<Z>cest|utc|cet|gmt)This is propably only true for my local timezone as is EST for yours :-). Switching to numeric timezones should do the trick.
Regards Mirko