"end Kernel Panic" error on boot-up after upgrading Ubuntu

[illorenzo]

Hi all,

I was running Virtualbox 4.3.28 on Macbook Pro. OS: Mac OSX Yosemite 10.10.2, Processor: 2.9 GHz Intel Core i5. Memory: 8 GB 1867 MHz DDR3. My guest system was Ubuntu 14.04 (with Guest Additions installed) but I recently upgraded to Ubuntu 15.04. There is 4 GB of RAM allocated to Ubuntu. Both are 64-bit operating systems. There was a problem with the upgrade, and the virtual machine froze, so I "powered it off." Ever since then I've beens getting the same "end Kernel Panic not syncing! -- Attempted to kill Init" error (please see the attached screenshot for more details) when I try to boot the virtual machine. I tried unmounting the guest additions, upgrading to Virtualbox 5.08, and searched for a similar problem on the forums but haven't found anything! I also have since updated the Mac OS to El Capitan 10.11.1 (not sure if this was a good or bad idea).

If anyone has any insight as to how I can successfully boot the machine and recover my data, I would be incredibly appreciative!

Thank you very much,

illorenzo