Panos, Ordinal in this context is the y values. It's not the
> length of the y array, it's the values in the array. Dates
> are days past some epoch and dates before the epoch are not
> allowed. Maybe you're getting a date value that's < 1 which
> is what is causing the problem. Are you plotting dates on
> the y axis anywhere?
Here ordinal is used in the sense of the python datetime toordinal
method, not in the ordinal / abscissa of the y / x axis. Admittendly
ambiguous. But I think your first comment is spot on: probably an
illegal ordinal value is used, eg
import datetime
print datetime.datetime.fromordinal(1)
print datetime.datetime.fromordinal(0)
JDH