@kiwidude: I've had the same issues as ash600 since 1.6.x.
The following quick & dirty patch seems to fix it, although you get a successful dialog even when it fails to get a pagecount from Goodreads (the failure is visible in the log/details, and clicking yes effectively does nothing). Since it was good enough for me (and I suck at Python), I haven't looked at it further
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From what I can gather, when running a goodreads download job, book_path is unset (None), but the plugin attempts to use it unconditionally to get the file extension => kablooey.
EDIT: Killed deprecated attachments. Fix merged upstream.