Per the magic item creation rules:
Creating a magic weapon has a special prerequisite: The creator's caster level must be at least three times the enhancement bonus of the weapon. If an item has both an enhancement bonus and a special ability, the higher of the two caster level requirements must be met. A magic weapon must have at least a 1 enhancement bonus to have any melee or ranged special weapon abilities.
So what is the caster level requirement to create a Sun Blade?
Is it 6 (3 x its normal +2 enhancement bonus), 12 (3 x its +4 enhancement bonus when used vs evil) or something else keyed off one of its other properties?