Problem installing kernel due to virtualbox?

[John Whitmore]

I've been AWOL working on other things for an age, so just getting back up to speed and building a kernel. Everything built successfully but when I try to install the kernel (64bit laptop) it fails due to a virtualbox error.

  ERROR (dkms apport): kernel package linux-headers-4.16.0-rc5 is not supported
  Error! Bad return status for module build on kernel: 4.16.0-rc5 (x86_64)
  Consult /var/lib/dkms/virtualbox/5.0.40/build/make.log for more information.

I've had a look at that log file but it doesn't say a whole lot more:

  ...linux/scripts/Makefile.build:583: recipe for target '/var/lib/dkms/virtualbox/5.0.40/build/vboxdrv' failed
  make[5]: *** [/var/lib/dkms/virtualbox/5.0.40/build/vboxdrv] Error 2
  Makefile:1552: recipe for target '_module_/var/lib/dkms/virtualbox/5.0.40/build' failed
  make[4]: *** [_module_/var/lib/dkms/virtualbox/5.0.40/build] Error 2
  Makefile:24: recipe for target '__sub-make' failed
  make[3]: *** [__sub-make] Error 2

An Internet search did throw up a few pages about a virtualbox error [1] but I'm not sure the relevance to installing a Linux Kernel. Unless 'sudo make install' is running an Ubuntu script which tries to mess with virtual box. I have removed virtualbox from this machine and tried again but I've still got the same error message in the install process. Maybe I have to reboot after removing virtualbox but it still seems a bit tightly coupled? 

[1] https://bugs.launchpad.net/ubuntu/+source/virtualbox/+bug/1729568