I was running Virtual Box 5.2.22 under Ubuntu 16.04. After my employer updated the kernel, VB ceased to work (kernel modules). After following the instructions provided by the error message, I thought I'd try a newer version of VB. I installed 6.0.8.
VB 6.0.8 solved the problem but now I have a problem with very small text size on the VirtualBox "control" window on a 2560x1440 display. If I try a 1920x1080 screen, the text is "normal" size but that isn't a viable long term solution.
When I launch a Guest O/S the title bar is fine and the guest O/S works fine. The text size inside the Guest O/S is fine. However, the VB menu bar in that window is small. (The guest O/S versions that I tested are Ubuntu 16.04 and 18.04 as well as CentOS 7.6.)
Every other program that I've run on this computer has text that I can read. So far, it is just VirtualBox 6.0.8.
I found one page that suggested I increase the scaling size to 200% but that changed the scaling size inside the Guest O/S; not for the VB menus. I didn't find a control for the menu size. Attempting to change the scale for Title and Menu bars in the Host O/S worked had the expected effect on other programs but not on VirtualBox.