System.ArgumentException: An item with the same key has already been added
I submit my data entry form then it throw an exception for me: 

Can anyone show me what happen? I try to find out where it duplicated, but no answer. 



[ArgumentException: An item with the same key has already been added.]
   System.ThrowHelper.ThrowArgumentException(ExceptionResource resource) +51
   System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add) +7460188
   System.Linq.Enumerable.ToDictionary(IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer) +270
   System.Linq.Enumerable.ToDictionary(IEnumerable`1 source, Func`2 keySelector, IEqualityComparer`1 comparer) +102
   System.Web.Mvc.ModelBindingContext.get_PropertyMetadata() +228
   System.Web.Mvc.DefaultModelBinder.BindProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, PropertyDescriptor propertyDescriptor) +381
   System.Web.Mvc.DefaultModelBinder.BindProperties(ControllerContext controllerContext, ModelBindingContext bindingContext) +144
   System.Web.Mvc.DefaultModelBinder.BindComplexElementalModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Object model) +95
   System.Web.Mvc.DefaultModelBinder.BindComplexModel(ControllerContext controllerContext, ModelBindingContext bindingContext) +2386
   System.Web.Mvc.DefaultModelBinder.BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) +539
   System.Web.Mvc.Controller.TryUpdateModel(TModel model, String prefix, String[] includeProperties, String[] excludeProperties, IValueProvider valueProvider) +744
   System.Web.Mvc.Controller.TryUpdateModel(TModel model) +139
   LDC.Controllers.StorageController.Add(FormCollection form) in D:\Projects\Letgo3.0\LDC.Web\Controllers\StorageController.cs:142
   lambda_method(ExecutionScope , ControllerBase , Object[] ) +140
   System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters) +51
   System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters) +406
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters) +49
   System.Web.Mvc.<>c__DisplayClassd.<InvokeActionMethodWithFilters>b__a() +124
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation) +421
   System.Web.Mvc.<>c__DisplayClassf.<InvokeActionMethodWithFilters>b__c() +61
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList`1 filters, ActionDescriptor actionDescriptor, IDictionary`2 parameters) +305
   System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +801
   System.Web.Mvc.Controller.ExecuteCore() +151
   System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +105
   System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext) +36
   System.Web.Mvc.<>c__DisplayClass8.<BeginProcessRequest>b__4() +65
   System.Web.Mvc.Async.<>c__DisplayClass1.<MakeVoidDelegate>b__0() +44
   System.Web.Mvc.Async.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _) +42
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +140
   System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +54
   System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +40
   System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +52
   System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +36
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8674318
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155

System.ArgumentException: An item with the same key has already been added
===

I submit my data entry form then it throw an exception for me: 

Can anyone show me what happen? I try to find out where it duplicated, but no answer. 



[ArgumentException: An item with the same key has already been added.]
   System.ThrowHelper.ThrowArgumentException(ExceptionResource resource) +51
   System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add) +7460188
   System.Linq.Enumerable.ToDictionary(IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer) +270
   System.Linq.Enumerable.ToDictionary(IEnumerable`1 source, Func`2 keySelector, IEqualityComparer`1 comparer) +102
   System.Web.Mvc.ModelBindingContext.get_PropertyMetadata() +228
   System.Web.Mvc.DefaultModelBinder.BindProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, PropertyDescriptor propertyDescriptor) +381
   System.Web.Mvc.DefaultModelBinder.BindProperties(ControllerContext controllerContext, ModelBindingContext bindingContext) +144
   System.Web.Mvc.DefaultModelBinder.BindComplexElementalModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Object model) +95
   System.Web.Mvc.DefaultModelBinder.BindComplexModel(ControllerContext controllerContext, ModelBindingContext bindingContext) +2386
   System.Web.Mvc.DefaultModelBinder.BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) +539
   System.Web.Mvc.Controller.TryUpdateModel(TModel model, String prefix, String[] includeProperties, String[] excludeProperties, IValueProvider valueProvider) +744
   System.Web.Mvc.Controller.TryUpdateModel(TModel model) +139
   LDC.Controllers.StorageController.Add(FormCollection form) in D:\Projects\Letgo3.0\LDC.Web\Controllers\StorageController.cs:142
   lambda_method(ExecutionScope , ControllerBase , Object[] ) +140
   System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters) +51
   System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters) +406
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters) +49
   System.Web.Mvc.<>c__DisplayClassd.<InvokeActionMethodWithFilters>b__a() +124
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation) +421
   System.Web.Mvc.<>c__DisplayClassf.<InvokeActionMethodWithFilters>b__c() +61
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList`1 filters, ActionDescriptor actionDescriptor, IDictionary`2 parameters) +305
   System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +801
   System.Web.Mvc.Controller.ExecuteCore() +151
   System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +105
   System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext) +36
   System.Web.Mvc.<>c__DisplayClass8.<BeginProcessRequest>b__4() +65
   System.Web.Mvc.Async.<>c__DisplayClass1.<MakeVoidDelegate>b__0() +44
   System.Web.Mvc.Async.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _) +42
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +140
   System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +54
   System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +40
   System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +52
   System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +36
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8674318
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155
