Most skills take MP to perform. The amount of MP used for each skill can vary from skill to skill. Lacking the MP needed to perform a Skill will result in that skill being grayed out in the skill bars.
Whether it’s a self-enhancement skill or a powered attack, each skill has its own properties and rules. Descriptions of these skills can be found by simply scrolling over the skill icon. Not meeting specific requirements for the skill before its use may lead to the skill being grayed out.
Most skills in the game have a certain range in which they must be performed in. Not being appropriate range will show the skill being grayed out.
If, however, the skill is grayed out and all of these other situations have been checked, please submit a ticket to Support for additional assistance. Information you will want to include are:
Screenshots: (if possible)
Description of issue: