I am getting this error
When i am killing the enemy
ArgumentException: GetComponent requires that the requested component ‘Item’ derives from MonoBehaviour or Component or is an interface.

My Script:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

/* This makes our enemy interactable. */

public class Enemy : Interactable {

	CharacterStats stats;
	public RagdollManager ragdoll;

    public GameObject Sword;//your sword
    private void OnDestroy() //called, when enemy will be destroyed
    void Start ()
		stats = GetComponent<CharacterStats>();
		stats.OnHealthReachedZero += Die;

	// When we interact with the enemy: We attack it.
	public override void Interact()
		print ("Interact");
		CharacterCombat combatManager = Player.instance.playerCombatManager;

	void Die() {
		ragdoll.transform.parent = null;
		ragdoll.Setup ();
		Destroy (gameObject);


my inventory it static

Both your Item class, and your CharacterStats class should inherit (directly or indirectly) from MonoBehavior/NetworkBehavior. Double-check their ancestry to see if this is the case.