title: ArgumentException: An element with the same key already exists in the dictionary
body: <p>In my project, I got two scene 'Opening' 'Main'.  </p>
  
  <p>If there's no keydown in put for a while or complete the task,<br>
  It will go back to Opening scene and can start again.  </p>
  
  <p>It works, to go Opening scene -> Main scene<br>
  and go to the Main scene -> Opening scene  </p>
  
  <p>However 'Main scene -> Opening scene' and when I try to go Main scene again,<br>
  It shows these error. :</p>
  
  <pre class="lang-none prettyprint-override"><code>ArgumentException: An element with the same key already exists in the dictionary.
  System.Collections.Generic.Dictionary`2[System.Int32,System.Collections.Generic.Dictionary`2[KeyDelayData+Delay,UnityEngine.Sprite]].Add (Int32 key, System.Collections.Generic.Dictionary`2 value) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Collections.Generic/Dictionary.cs:404)
  Note.Init () (at Assets/Scripts/Music/Note.cs:22)
  ManagerChat.Awake () (at Assets/Scripts/Chatting/ManagerChat.cs:315)
  
  ArgumentException: An element with the same key already exists in the dictionary.
  System.Collections.Generic.Dictionary`2[System.Int32,UnityEngine.AudioClip].Add (Int32 key, UnityEngine.AudioClip value) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Collections.Generic/Dictionary.cs:404)
  SoundManager.Awake () (at Assets/Scripts/Music/SoundManager.cs:16)
  </code></pre>
  
  <p>It looks like some resetting variable issue for me but I don't know what it mean<br>
  What can I do to fix this? </p>