Taking an upgrade (from pve-manager 4.4-5 to 4.4-12) broke PVE, since the file "/usr/share/perl5/PVE/VZDump/Plugin.pm" was missing from the .deb for 4.4-12. I "solved" this by copying it from the .deb for 4.4-5. Hopefully you can address this regression soon.
proxmox-ve: 4.4-79 (running kernel: 4.4.35-2-pve)
pve-manager: 4.4-12 (running version: 4.4-12/e71b7a74)
pve-kernel-4.4.35-2-pve: 4.4.35-78
lvm2: 2.02.111-2.2+deb8u1
corosync-pve: 2.4.0-1
libqb0: 1.0-1
pve-cluster: 4.0-48
qemu-server: 4.0-102
pve-firmware: 1.1-10
libpve-common-perl: 4.0-85
libpve-access-control: 4.0-19
libpve-storage-perl: 4.0-71
pve-libspice-server1: 0.12.8-1
vncterm: 1.2-1
pve-docs: 4.4-1
pve-qemu-kvm: 2.7.1-1
pve-container: 1.0-90
pve-firewall: 2.0-33
pve-ha-manager: 1.0-38
ksm-control-daemon: 1.2-1
glusterfs-client: 3.5.2-2+deb8u3
lxc-pve: 2.0.6-5
lxcfs: 2.0.5-pve2
criu: 1.6.0-1
novnc-pve: 0.5-8
smartmontools: 6.5+svn4324-1~pve80
proxmox-ve: 4.4-79 (running kernel: 4.4.35-2-pve)
pve-manager: 4.4-12 (running version: 4.4-12/e71b7a74)
pve-kernel-4.4.35-2-pve: 4.4.35-78
lvm2: 2.02.111-2.2+deb8u1
corosync-pve: 2.4.0-1
libqb0: 1.0-1
pve-cluster: 4.0-48
qemu-server: 4.0-102
pve-firmware: 1.1-10
libpve-common-perl: 4.0-85
libpve-access-control: 4.0-19
libpve-storage-perl: 4.0-71
pve-libspice-server1: 0.12.8-1
vncterm: 1.2-1
pve-docs: 4.4-1
pve-qemu-kvm: 2.7.1-1
pve-container: 1.0-90
pve-firewall: 2.0-33
pve-ha-manager: 1.0-38
ksm-control-daemon: 1.2-1
glusterfs-client: 3.5.2-2+deb8u3
lxc-pve: 2.0.6-5
lxcfs: 2.0.5-pve2
criu: 1.6.0-1
novnc-pve: 0.5-8
smartmontools: 6.5+svn4324-1~pve80