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In order to run Owl under VirtualBox OSE you should enable 'Physical Address Extension' (PAE).
If this option is not enabled you will get an error like this:
Unknown interrupt or fault at EIP 00000060 c09671f5 000071f4
Select 'Machine→Settings' from the menu (or: CTRL+S). Then select 'System', then the 'Processor' tab. Finally, check/click 'Enable PAE/NX' and click 'OK'.