Solution :
Finally I am able to find the fix for your issue now.
Firstly, you need to understand your problem which mostly people not really find out, it seems your VM came with guest OS of Ubuntu 64-bits but after doing the import, you must have checked on that VM which shows only 32-bits OS.
And when you start the VM, you must have got below error :
Failed to open a session for the virtual machine ERPNext-Develop-20180331192506.
Raw-mode is unavailable courtesy of Hyper-V. (VERR_SUPDRV_NO_RAW_MODE_HYPER_V_ROOT).
Result Code: E_FAIL (0x80004005)
Component: ConsoleWrap
Interface: IConsole {872da645-4a9b-1727-bee2-5585105b9eed}
I realized that the point above (32-bits OS) so I thought the problem must be with this one.
After doing the research I understood that Windows 10 also comes up with the Hyper-V which is conflicting with your Oracle VM VirtualBox.
So solution for you as below...
1. Disable the Virtualization Based Security in group policy
· Start and Run application and start the gpedit.msc
· Go to your Computer configuration > Administrative Template > Device Guard
2. Disable the Microsoft Hyper-V
· Start and Run application and start the OptionalFeatures.exe
· Untick the Hyper-V
· Restart your PC
Now you can use the VM, it must be started.