It is a RAM related issue. The documentation is self explanatory:
You are trying to allocate >3GB of RAM to the VM. This requires: (a) a
64 bit host system; and (b) true hardware pass-through ie VT-x.
Fast solution
Allocate less than 3GB for the virtual machine.
Complete solution
- Make sure your system is 64 bit.
- Enable virtualisation in your host machine. You can find how to do it here or there are many other resources available on Google.