Enable PAE in Virtual Box

On my second attempt to install Virtual Box Ubuntu on my old laptop with Windows XP as a host, I encountered this error on booting:

1. This kernel requires the following features not present on the CPU:
pae
Unable to boot - please use a kernel appropriate for your CPU.

2. Solution: Shut down the machine. Go to Ubuntu settings, select "System"on left column, select "Processor" tab on the right, check Enable PAE/NX.

Click  ok. Solved. The Ubuntu can boot bow.