Hi I have a QNAP419P+ with Debian 8 firmware. I have installed ODOO 8 following instructions from here http://www.theopensourcerer.com/2014/09/how-to-install-openerp-odoo-8-on-ubuntu-server-14-04-lts/

All went OK but when I try to pint invoice I get an error

Wkhtmltopdf failed (error code: -6). Message: The switch --header-spacing, is not support using unpatched qt, and will be ignored.The switch --header-html, is not support using unpatched qt, and will be ignored.The switch --footer-html, is not support using unpatched qt, and will be ignored.QXcbConnection: Could not connect to display 

If I go under settings -> general settings -> Configure your company data -> report configuration the preview header/footer work OK.

I was searching around but could not get clear answer. Because the Qnap 419 p+ uses ARM processor. So I am kind of stuck. 

Any help how to solve this issue would be more than appreciated. :)

data sheet to qnap

http://files.qnap.com/news/pressresource/datasheet/Home_SOHO_NAS_datasheet_EN.pdf

cheers Ziga