I have the same problems with:
Kernel 4.4.0-143-generic
Virtualbox 5.2.26 r128414
Ubuntu 16.04.6 LTS
My workaround:
Select previous Kernel 4.4.0-142-generic through "GRUB Customizer".
Reboot.
No rebuild/reinstall of VBox components neccessary.
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Some additional information:
Downgrading to 0.6.1-2 fixes the problem for me,too.
Disabling "require-encryption" via "org.gnome.Vino" doesn't help.
When you run "xrdp -ns", there is only one message in case of the fault:
"loaded module 'libvnc.so' ok, interface size 4040, version 2
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