Missing Reference Exception Error

I'm getting this error when I try to add multiple clip to the Master Audio prefab:

MissingReferenceException: The variable audioSourceTemplates of MasterAudio doesn't exist anymore.
You probably need to reassign the audioSourceTemplates variable of the 'MasterAudio' script in the inspector.
UnityEngine.Object.get_name () (at <7c9c9bc2498143d08e2e3c523ff86731>:0)
DarkTonic.MasterAudio.EditorScripts.MasterAudioInspector+<>c.<get_SelectedAudioSourceTemplate>b__60_0 (UnityEngine.GameObject obj) (at Assets/Plugins/Editor/DarkTonic/MasterAudio/MasterAudioInspector.cs:7933)
System.Collections.Generic.List`1[T].Find (System.Predicate`1[T] match) (at <eae584ce26bc40229c1b1aa476bfa589>:0)
DarkTonic.MasterAudio.EditorScripts.MasterAudioInspector.get_SelectedAudioSourceTemplate () (at Assets/Plugins/Editor/DarkTonic/MasterAudio/MasterAudioInspector.cs:7931)
DarkTonic.MasterAudio.EditorScripts.MasterAudioInspector.CopyFromAudioSourceTemplate (UnityEngine.AudioSource oldAudSrc, System.Boolean showError) (at Assets/Plugins/Editor/DarkTonic/MasterAudio/MasterAudioInspector.cs:7942)
DarkTonic.MasterAudio.EditorScripts.MasterAudioInspector.CreateSoundGroup (System.String soundGroupName, System.String variationName, UnityEngine.AudioClip aClip) (at Assets/Plugins/Editor/DarkTonic/MasterAudio/MasterAudioInspector.cs:6629)
DarkTonic.MasterAudio.EditorScripts.MasterAudioInspector.OnInspectorGUI () (at Assets/Plugins/Editor/DarkTonic/MasterAudio/MasterAudioInspector.cs:2117)
UnityEditor.UIElements.InspectorElement+<>c__DisplayClass58_0.<CreateIMGUIInspectorFromEditor>b__0 () (at <fc4e84dee5004858ad88e6706bb25889>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)