Comment 1 for bug 404019

I'm assuming you're using Ubuntu Karmic, which brings a new unstable release of GTK+ and its new incompatible changes in the XInput event processing. Try applying to the source code the two patches at
http://sourceforge.net/tracker/?func=detail&aid=2829716&group_id=163434&atid=827735
(should fix the difficulties of drawing with devices other than tablet pens)
and
http://sourceforge.net/tracker/?func=detail&aid=2816361&group_id=163434&atid=827735
(for the latter one: the revised version that says "also fixes menu issues in GTK+ 2.17")

Hope this helps,
Denis