You must target a specific version of Virbox. The VM handlers change with every minor update. Your unpacker will break next week.

Before attempting to unpack, you must identify which layers are active. Virbox Protector commonly employs: Virtualization (VME):

If critical logic was virtualized using Virbox’s VME, the dumped code will still contain VM calls. Unpacking this requires writing a custom "devirtualizer" to translate the VM bytecode back into x86/x64 instructions—a task that can take weeks of expert work. Official Resources & Documentation

Unpacking Virbox Protector involves overcoming several multi-layered defense mechanisms: