Originally Posted by khromov
I could not reproduce your issue using the Calibre GUI on windows with either the stable or dev version.
I also tried running the command-line version on a Debian install and couldn't reproduce that either.
Can you verify that you are still getting this error, and in that case could you try another Instapaper account to make sure this is not a particular article tripping Calibre up?
Thanks, will give it a go and let you know.