help me exception on asp.net mvc 4

The underlying provider failed on Open. —> System.InvalidOperationException: The connection was not closed. The connection’s current state is connecting.
at System.Data.ProviderBase.DbConnectionClosedConnecting.TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource1 retry, DbConnectionOptions userOptions) at System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource1 retry)
at System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource1 retry) at System.Data.SqlClient.SqlConnection.Open() at System.Data.Entity.Infrastructure.Interception.InternalDispatcher1.Dispatch[TTarget,TInterceptionContext](TTarget target, Action2 operation, TInterceptionContext interceptionContext, Action3 executing, Action3 executed) at System.Data.Entity.Infrastructure.Interception.DbConnectionDispatcher.Open(DbConnection connection, DbInterceptionContext interceptionContext) at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.<>c__DisplayClass1.<Execute>b__0() at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func1 operation)
at System.Data.Entity.Core.EntityClient.EntityConnection.Open()
— End of inner exception stack trace —
at System.Data.Entity.Core.EntityClient.EntityConnection.Open()
at System.Data.Entity.Core.Objects.ObjectContext.EnsureConnection(Boolean shouldMonitorTransactions)
at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess) at System.Data.Entity.Core.Objects.ObjectQuery1.<>c__DisplayClass7.b__5()
at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func1 operation) at System.Data.Entity.Core.Objects.ObjectQuery1.GetResults(Nullable1 forMergeOption) at System.Data.Entity.Core.Objects.ObjectQuery1.<System.Collections.Generic.IEnumerable.GetEnumerator>b__0()
at System.Data.Entity.Internal.LazyEnumerator1.MoveNext() at System.Collections.Generic.List1..ctor(IEnumerable1 collection) at System.Linq.Enumerable.ToList[TSource](IEnumerable1 source)
at Erp.BackOffice.Sale.Controllers.PlanningOfProductionController.IndexProduction(String Code, String ProductCode, String ProductName, String CustomerName, String InvoiceCode, String Type, Nullable1 IsInvoiceChange, Nullable1 salerId, String fromCreateDate, String toCreateDate, String CustomerProductCode, String CustomerProductName) in D:nqherpErp.BackOfficeAreasSaleControllersPlanningOfProductionController.cs:line 255
at lambda_method(Closure , ControllerBase , Object[] )
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary2 parameters) at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c.<BeginInvokeSynchronousActionMethod>b__9_0(IAsyncResult asyncResult, ActionInvocation innerInvokeState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult2.CallEndDelegate(IAsyncResult asyncResult)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.<>c__DisplayClass11_0.b__0()
at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.<>c__DisplayClass11_2.b__2()
at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.<>c__DisplayClass11_2.b__2()
at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.<>c__DisplayClass11_2.b__2()
at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.<>c__DisplayClass11_2.b__2()
at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.<>c__DisplayClass11_2.b__2()
at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.<>c__DisplayClass11_2.b__2()
at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethodWithFilters(IAsyncResult asyncResult)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass3_6.b__4()
at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass3_1.b__1(IAsyncResult asyncResult)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult)
at System.Web.Mvc.Controller.<>c.b__152_1(IAsyncResult asyncResult, ExecuteCoreState innerState)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid1.CallEndDelegate(IAsyncResult asyncResult) at System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid1.CallEndDelegate(IAsyncResult asyncResult)
at System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult)
at System.Web.Mvc.MvcHandler.<>c.b__20_1(IAsyncResult asyncResult, ProcessRequestState innerState)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult)
at System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult)
at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step)
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Error was always happening