It sounds like you don't have the GD extension installed. I don't use Ubuntu any longer, but I think it may be named php5-gd,...
The instructions @ericklan posted are on the right track, though they aren't quite clear to me and seem to recommend more than is necessary....
Filesystem-Passthrough
Use virt-manager to share files between Linux host and Windows guest? I usually setup a Samba server on the Linux KVM host and then share a folder out using that to my KVM guests.
1. Configure Proxy Clients Configure proxy settings like follows on Debian Client. root@client:~# vi /etc/profile # add follows to the end (set proxy settings...