Detected Hardware Unit Hang:
The version of the driver is significatly old, so I downloaded the newest from Sourceforge and tried to compile it. It failed to compile do to some power management code that is not in the kernel source from Debian. Eventually I found someone else who'd had the same problem with the igb driver and solved it just by adding a flag to make: CFLAGS_EXTRA=-DDISABLE_PM
Did the same when building the e1000e driver, compiled smoothly, remade initramfs, rebooted, haven't seen an error since.