Couldn't resolve host

Hi, i have a problem qith wp installed to my host (hostgator.com)

I have this error in my dashboard:
Errore RSS: WP HTTP Error: Couldn’t resolve host ‘ww.wp.xz.cn’

and i cant download and install plugin.

My site is http://www.spaggiari-srl.com

Until now the software work perfectly.

Thank you