Can't return Enum state to script

Hi,

I am building a multi-class game and I have a small enum FSM. I decided to split the FSM into another "Players" script, while I have another script named "UI". "UI" accesses this Players script.

I've never attempted to return an Enum type, so i've never experienced an error like this before. The error I get is "UI.cs | A constant value is expected | Line 52". I don't understand why it would need to be constant. If I place the Enum in the UI.cs file, the problem goes away. I don't understand why it is any different from another script file.

Perculiarly, I don't get the error with the following code block commented out in Players.cs:

  */void Start ()
  {
      PlayersTurn = TurnStates.Player_1_Turn;
  }*/

Players.cs

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Players : MonoBehaviour {
 
     public static Players Script;
 
     public enum TurnStates { Player_1_Turn, Player_2_Turn };
 
     #region PLAYER FSM
     TurnStates PlayersTurn;
     #endregion
 
    void Awake()
     {
         Script = this;
     }

     /*
     // Use this for initialization
     void Start ()
     {
         PlayersTurn = TurnStates.Player_1_Turn;
     }*/
     
     // Update is called once per frame
     void Update () {
         
     }
 
     public TurnStates getPlayerTurnState()
     {
         return PlayersTurn;
     }
 
     public void setPlayerTurnState(TurnStates State)
     {
         PlayersTurn = State;
     }
 
     public TurnStates getPossibleTurnState_P1()
     {
         return TurnStates.Player_1_Turn;
     }
 
     public TurnStates getPossibleTurnState_P2()
     {
         return TurnStates.Player_2_Turn;
     }
 }

UI.cs

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class UI : MonoBehaviour {
 
     public static UI Script;
 
     #region UI
     // Used to Display Time Passed since Game session start
     public Text txtTimePlayed;
     string TimeText = "Session Time: ";
     int Time_Integer;           // Hold Time.time integer from float
 
     // Used to Display the amount of convoys in accordance with the Player FSM
     public Text txtYourConvoys;
     string YourConvoyText = "Your Convoys: ";
 
     // Used to Display the current Players Turn with various variables
     public Text txtPlayerTurn;
     string PlayerTurnString = "Current Turn: ";
     string Player1_Turn_Text = "Player 1";
     string Player2_Turn_Text = "Player 2";
     #endregion
 
     void Awake()
     {
         Script = this;
     }
 
     void Start ()
     {
 
     }
     
     void Update ()
     {
         
     }
 
     public void update_SessionTime()
     {
         Time_Integer = (int)Time.time;
         txtTimePlayed.text = TimeText + Time_Integer.ToString();
     }
 
     public void Update_Convoys_And_PlayerTurn()
     {
         switch (Players.Script.getPlayerTurnState())
         {
             case Players.Script.getPossibleTurnState_P1():
                 txtYourConvoys.text = YourConvoyText + Player_1_Convoys.ToString();
                 txtPlayerTurn.text = PlayerTurnString + Player1_Turn_Text;
                 break;
             case Players.Script.getPossibleTurnState_P2():
                 txtYourConvoys.text = YourConvoyText + Player_2_Convoys.ToString();
                 txtPlayerTurn.text = PlayerTurnString + Player2_Turn_Text;
                 break;
         }
     }
 }