Coroutine couldn't be started because the the game object 'Attack' is inactive!

Hi everyone, this question is a bit long, but please bear with me.

I'm creating a game with a combat system very similar to final fantasy 10. I'm a big fan of keeping my code as neat as possible, so my characters all derive from a basic character class. that class contains a List of four abilities (as each character can only have four), which is of the type basicSkill, like this

     List<basicSkill> Skills = new List<basicSkill>();

I then created an empty prefab named Attack (for a basic attack) with only basicSkill as it's component. I then dragged this prefab into the List of skills in a characters' component.

within every skill is a Run() function. it's always named run so that no matter what skill it is, you can run it straight from the character's skills list by it's index in the list.

Run is seen below

     public void Run (GameObject attacker, GameObject target, _DefaultCharacter attackerStats, _DefaultCharacter targetStats){
         _damage = attackerStats.Damage / targetStats.armor;
         if (isMelee == true){
             StartCoroutine(MeleeSequence());
         }
     }

     IEnumerator MeleeSequence(){
         yield return new WaitForSeconds(3);
         Debug.Log(name + "Sequence Complete");
     }

Once I had that sorted out, I created a button in order to test out my attack by having first character and enemy in the list as parameters. I was able to run attack through a long and convoluted line which you can see below.

 if (GUI.Button(new Rect(10,10,50,20), "test attack")){
             allies[0].GetComponent<_DefaultCharacter>().newSkills[0].Run(allies[0], enemies[0], allies[0].GetComponent<_DefaultCharacter>(), enemies[0].GetComponent<_DefaultCharacter>());
         }

The problem is, I keep getting the error seen below;

 Coroutine couldn't be started because the the game object 'Attack' is inactive! 

I believe that the problem lies in the fact that it is a prefab that I drag to the inspector window on skills. when I have the same prefab in the scene and try to drag it into the inspector it won't allow it, though I don't see why it would accept it as a prefab. The whole reason I've done this is because I've tried to stop using dynamic calls, though I don't have any other ideas.

What might be causing the error?