Error The namespace '' already contains a definition for 'AAMode'.

I get this error : BCE0132: The namespace '' already contains a definition for 'AAMode'. I tried a lot of options but I can't find the solution!

 #pragma strict
     
     @script ExecuteInEditMode
     @script RequireComponent (Camera)
     @script AddComponentMenu ("Image Effects/Antialiasing (Fullscreen)")
     
     enum AAMode {
         FXAA2 = 0,
         FXAA3Console = 1,        
         FXAA1PresetA = 2,
         FXAA1PresetB = 3,
         NFAA = 4,
         SSAA = 5,
         DLAA = 6,
     }
     
     class AntialiasingAsPostEffect extends PostEffectsBase  {
         public var mode : AAMode = AAMode.FXAA3Console;
     
         public var showGeneratedNormals : boolean = false;
         public var offsetScale : float = 0.2;
         public var blurRadius : float = 18.0;
     
         public var edgeThresholdMin : float = 0.05f;
         public var edgeThreshold : float = 0.2f;
         public var edgeSharpness : float  = 4.0f;
             
         public var dlaaSharp : boolean = false;
     
         public var ssaaShader : Shader;
         private var ssaa : Material;
         public var dlaaShader : Shader;
         private var dlaa : Material;
         public var nfaaShader : Shader;
         private var nfaa : Material;    
         public var shaderFXAAPreset2 : Shader;
         private var materialFXAAPreset2 : Material;
         public var shaderFXAAPreset3 : Shader;
         private var materialFXAAPreset3 : Material;
         public var shaderFXAAII : Shader;
         private var materialFXAAII : Material;
         public var shaderFXAAIII : Shader;
         private var materialFXAAIII : Material;
             
         function CurrentAAMaterial () : Material
         {
             var returnValue : Material = null;
     
             switch(mode) {
                 case AAMode.FXAA3Console:
                     returnValue = materialFXAAIII;
                     break;
                 case AAMode.FXAA2:
                     returnValue = materialFXAAII;
                     break;
                 case AAMode.FXAA1PresetA:
                     returnValue = materialFXAAPreset2;
                     break;
                 case AAMode.FXAA1PresetB:
                     returnValue = materialFXAAPreset3;
                     break;
                 case AAMode.NFAA:
                     returnValue = nfaa;
                     break;
                 case AAMode.SSAA:
                     returnValue = ssaa;
                     break;
                 case AAMode.DLAA:
                     returnValue = dlaa;
                     break;    
                 default:
                     returnValue = null;
                     break;
                 }
                 
             return returnValue;
         }
     
         function CheckResources () {
             CheckSupport (false);
             
             materialFXAAPreset2 = CreateMaterial (shaderFXAAPreset2, materialFXAAPreset2);
             materialFXAAPreset3 = CreateMaterial (shaderFXAAPreset3, materialFXAAPreset3);
             materialFXAAII = CreateMaterial (shaderFXAAII, materialFXAAII);
             materialFXAAIII = CreateMaterial (shaderFXAAIII, materialFXAAIII);
             nfaa = CreateMaterial (nfaaShader, nfaa);
             ssaa = CreateMaterial (ssaaShader, ssaa); 
             dlaa = CreateMaterial (dlaaShader, dlaa); 
                     
             if(!ssaaShader.isSupported) {
                 NotSupported ();
                 ReportAutoDisable ();
             }
             
             return isSupported;                    
         }
     
         function OnDisable()
         {
             if(materialFXAAPreset2)
                 Destroy(materialFXAAPreset2);
             if(materialFXAAPreset3)
                 Destroy(materialFXAAPreset3);
             if(materialFXAAII)
                 Destroy(materialFXAAII);
             if(materialFXAAIII)
                 Destroy(materialFXAAIII);
             if(nfaa)
                 Destroy(nfaa);
             if(ssaa)
                 Destroy(ssaa);
             if(dlaa)
                 Destroy(dlaa);
         }
         
         function OnRenderImage (source : RenderTexture, destination : RenderTexture) {
             if(CheckResources()==false) {
                 Graphics.Blit (source, destination);
                 return;
             }
                     
              // .............................................................................
             // FXAA antialiasing modes .....................................................
             
             if (mode == AAMode.FXAA3Console && (materialFXAAIII != null)) {
                 materialFXAAIII.SetFloat("_EdgeThresholdMin", edgeThresholdMin);
                 materialFXAAIII.SetFloat("_EdgeThreshold", edgeThreshold);
                 materialFXAAIII.SetFloat("_EdgeSharpness", edgeSharpness);        
             
                 Graphics.Blit (source, destination, materialFXAAIII);
             }        
             else if (mode == AAMode.FXAA1PresetB && (materialFXAAPreset3 != null)) {
                 Graphics.Blit (source, destination, materialFXAAPreset3);
             }
             else if(mode == AAMode.FXAA1PresetA && materialFXAAPreset2 != null) {
                 source.anisoLevel = 4;
                 Graphics.Blit (source, destination, materialFXAAPreset2);
                 source.anisoLevel = 0;
             }
             else if(mode == AAMode.FXAA2 && materialFXAAII != null) {
                 Graphics.Blit (source, destination, materialFXAAII);
             }
             else if (mode == AAMode.SSAA && ssaa != null) {
     
             // .............................................................................
             // SSAA antialiasing ...........................................................
                 
                 Graphics.Blit (source, destination, ssaa);                                
             }
             else if (mode == AAMode.DLAA && dlaa != null) {
     
             // .............................................................................
             // DLAA antialiasing ...........................................................
             
                 source.anisoLevel = 0;    
                 var interim : RenderTexture = RenderTexture.GetTemporary (source.width, source.height);
                 Graphics.Blit (source, interim, dlaa, 0);            
                 Graphics.Blit (interim, destination, dlaa, dlaaSharp ? 2 : 1);
                 RenderTexture.ReleaseTemporary (interim);                    
             }
             else if (mode == AAMode.NFAA && nfaa != null) {
     
             // .............................................................................
             // nfaa antialiasing ..............................................
                 
                 source.anisoLevel = 0;    
             
                 nfaa.SetFloat("_OffsetScale", offsetScale);
                 nfaa.SetFloat("_BlurRadius", blurRadius);
                     
                 Graphics.Blit (source, destination, nfaa, showGeneratedNormals ? 1 : 0);                    
             }
             else {
                 // none of the AA is supported, fallback to a simple blit
                 Graphics.Blit (source, destination);                                
             }
         }
     }