"Type does not contain a definition for and no extension could be found" C#

I have been trying to get back into Unity development, and have been refreshing myself with a tutorial series. I’m having a problem with one of the segments though, it involves 2 scripts which inherit from another script, and I am receiving the error from the topic.

The error occurs on line 29, character 56 of ModifiedStat, however it references all the way back to BaseStat.

What can I do to fix this while maintaining the same basic flow so I can keep up with the tutorial series?

The scrips are as follows:

BaseStat:

using System;
using UnityEngine;


public class BaseStat{
	private int _baseValue;  //Unmodified stat
	private int _buffValue;   // after buffs
	private int _expToLevel;
	private float _levelModifier;

	public BaseStat()
	{
		_baseValue = 0;
		_buffValue = 0;
		_levelModifier = 1.1f;
		_expToLevel = 100;
	}

	//set get
#region set get
	public int BaseValue
	{
		get{return _baseValue;}
		set{_baseValue = value; }
	}
	public int BuffValue
	{
		get{return _buffValue;}
		set{_buffValue = value; }
	}
	public int ExpToLevel
	{
		get{return _expToLevel;}
		set{_expToLevel = value; }
	}
	public float LevelModifier
	{
		get{return _levelModifier;}
		set{_levelModifier = value; }
	}
#endregion

	private int CalculateExpToLevel()
	{
		return Mathf.FloorToInt((_expToLevel * _levelModifier)) ;
	}

	public void LevelUp()
	{
		_expToLevel = CalculateExpToLevel();
		_baseValue++;
	}

	public int AdjustedBaseValue
	{
		get{ return _baseValue + _buffValue;}
	}
}

Attribute:

using UnityEngine;
using System.Collections;

public class Attribute : BaseStat{

	public Attribute()
	{
		ExpToLevel = 50;
		LevelModifier = 1.05f;

	}
}

public enum AttributeName
{
	Might,
	Constitution,
	Nimbleness,
	Speed,
	Concentration,
	Willpower,
	Charisma
}

ModifiedStat:

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

public class ModifiedStat : BaseStat {

	private List<ModifyingAttribute> _mods;   //List of attributes that modify this stat
	private int _modValue;     //Amount added to the baseValue from the modifiers

	public ModifiedStat()
	{
		_mods = new List<ModifyingAttribute>();
		_modValue = 0;
	}

	public void AddModifier(ModifyingAttribute mod)
	{
		_mods.Add (mod);
	}

	private void CalculateModValue()
	{
		_modValue = 0;

		if(_mods.Count > 0)
		{
			foreach(ModifyingAttribute att in _mods)
			{
				_modValue += (int)(att.attribute.AdjustedBaseValue * att.ratio);
			}
		}
	}

	public new int AdjustedBaseValue 
	{
		get{ return BaseValue + BuffValue + _modValue;}
	}

	public void Update()
	{
		CalculateModValue();
	}
}

public struct ModifyingAttribute
{
	public Attribute attribute;
	public float ratio;
}

For some reason, my unity was just bugging out. I had some workaround, but others had said it worked for them, so I tried it again today, just commenting out what I had added to fix it yesterday, and ZERO errors.