MissingFieldException: UnityEngine.SpriteRenderer.sprite

this code should change a sprite to something from assets when...

 eval('PrizeSprite.GetComponent(SpriteRenderer).sprite = ' + '"NewFilesForGeometryGame/Characters/' + prize.ToString() + '"');

This Part of script is causing a problem and i don't know how to solve it. the error happen only when this code run during play when testing it.

error:

MissingFieldException: UnityEngine.SpriteRenderer.sprite Boo.Lang.Runtime.DynamicDispatching.PropertyDispatcherFactory.EmitPropertyDispatcher (System.Reflection.PropertyInfo property, SetOrGet gos) Boo.Lang.Runtime.DynamicDispatching.PropertyDispatcherFactory.EmitDispatcherFor (System.Reflection.MemberInfo info, SetOrGet gos) Boo.Lang.Runtime.DynamicDispatching.PropertyDispatcherFactory.Create (SetOrGet gos) Boo.Lang.Runtime.DynamicDispatching.PropertyDispatcherFactory.CreateSetter () Boo.Lang.Runtime.RuntimeServices.DoCreatePropSetDispatcher (System.Object target, System.Type type, System.String name, System.Object value) Boo.Lang.Runtime.RuntimeServices.CreatePropSetDispatcher (System.Object target, System.String name, System.Object value) Boo.Lang.Runtime.RuntimeServices+c_AnonStorey19.<>m_F () Boo.Lang.Runtime.DynamicDispatching.DispatcherCache.Get (Boo.Lang.Runtime.DynamicDispatching.DispatcherKey key, Boo.Lang.Runtime.DynamicDispatching.DispatcherFactory factory) Boo.Lang.Runtime.RuntimeServices.GetDispatcher (System.Object target, System.String cacheKeyName, System.Type[] cacheKeyTypes, Boo.Lang.Runtime.DynamicDispatching.DispatcherFactory factory) Boo.Lang.Runtime.RuntimeServices.GetDispatcher (System.Object target, System.Object[] args, System.String cacheKeyName, Boo.Lang.Runtime.DynamicDispatching.DispatcherFactory factory) Boo.Lang.Runtime.RuntimeServices.SetProperty (System.Object target, System.String name, System.Object value) script.Run () UnityScript.Scripting.Evaluator.Run () UnityScript.Scripting.Evaluator.Eval (UnityScript.Scripting.EvaluationContext context, System.String code) RandomPrize.AntiRepeat () (at Assets/Script/Money_shop/RandomPrize.js:82) RandomPrize+$RandomPrize$22+$.MoveNext () (at Assets/Script/Money_shop/RandomPrize.js:48)