Latest (4.4.0-53) kernel fails to boot - kernel panic

[Chris Green]

My old[ish] Acer Aspire netbook running 16.04.1 has just upgraded
itself to the 4.4.0-53 kernel, it crashes at startup with a kernel
panic, which ends as follows:-

  ---[ end kernel] panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

Fortunately the 4.4.0-51 kernel is still installed and still works
fine if selected from the boot menu 'advanced' options.

I looked at the grub.cfg file and the entries for 4.4.0-53 and
4.4.0-51 look the same (apart from the number difference) so I don't
really understand what's gone wrong, unless the 4.4.0-53 kernel really
is broken.

Is it possible I have a corrupted 4.4.0-53 installation or is there
some rather more obvious possibility?

Any/all ideas welcome.

-- 
Chris Green