When I run the executable \"wkhtmltopdf-amd64\" (from Linux), I get the following output:
QPainter::begin(): Returned false============================] 100%
I had the same problem.
"You're probably missing the 32bit libraries. Try: sudo aptitude install ia32-libs" - http://code.google.com/p/wkhtmltopdf/wiki/static
Worked for me