I recently installed Ubuntu 14.04 on a Xen HVM, and oddly, the network refused to work. It took a few searches, but I eventually ended up with https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=673043
Apparently, a end of line comment with my subnet had been added to my netmask (not sure if this is a ubuntu thing or a solusvm thing)
Removing the line allowed my VM to boot and configure its network properly.