Then it should be a relative path and not such an absolute one you have.
In one windows machine that has a qcow2 file for the virtual hdd, I have:
bootdisk: ide0
cores: 1
cpu: kvm32
ide0: local:150/vm-150-disk-0.qcow2,size=32G
ide2: none,media=cdrom
memory: 1024
name: WinXPN01
net0...