After a trail on error i collected these commands to solve it. Please check the result of dkms status first! this will show you the status of the installed kernel modules. This one is probably empty or showing errors
First uninstall the plugin. Then login to your openmediavault as root using ssh
Now the output of dkms status shows something like virtualbox, 5.2.24, 4.19.0-0.bpo.5-amd64, x86_64: installed. Right now you are good to go an reinstall the plugin.
Hope I could help you guys out!