If a character has Killer's Blade morphed, the skill shows up with a lock icon. This is because, when the skill was moved later in the Assassination skill line, the amount of experience needed to morph the skill was increased, but existing characters kept the amount of experience they had on the skill. Since Killer's Blade was previously the first skill in the line and required very little experience to morph, characters now have insufficient experience to morph the skill--hence, the morphs are "illegal."
While the morphed skills can be cast, the player cannot change morphs. Leveling the base skill until it can be morphed removes the lock icon and causes the skill to function normally.
In the future, when skills are shuffled around in the skill lines, they need to retain the
rank of the skill, not the
absolute value of gained experience.