Error save transaction entity framewok

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entity-framework

HI
I Have a problem to save transaction in two table header -details
the next codigo error is the following:


Thanks for the help me



System.Data.Entity.Core.EntityException was unhandled
HResult=-2146233087
Message=The underlying provider failed on Commit.
Source=EntityFramework
StackTrace:
en System.Data.Entity.Core.EntityClient.EntityTransaction.Commit()
en System.Data.Entity.DbContextTransaction.Commit()
en Cotizacion_Clientes.Cotizaciones.button2_Click(Object sender, EventArgs e) en E:\PROYECTOS_VS2015\Cotizacion_Clientes\Cotizacion_Clientes\Cotizaciones.cs:línea 64
en System.Windows.Forms.Control.OnClick(EventArgs e)
en System.Windows.Forms.Button.OnClick(EventArgs e)
en System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
en System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
en System.Windows.Forms.Control.WndProc(Message& m)
en System.Windows.Forms.ButtonBase.WndProc(Message& m)
en System.Windows.Forms.Button.WndProc(Message& m)
en System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
en System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
en System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
en System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
en System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
en System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
en System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
en System.Windows.Forms.Application.RunDialog(Form form)
en System.Windows.Forms.Form.ShowDialog(IWin32Window owner)
en System.Windows.Forms.Form.ShowDialog()
en Cotizacion_Clientes.Seleccione_Empresa.button1_Click(Object sender, EventArgs e) en E:\PROYECTOS_VS2015\Cotizacion_Clientes\Cotizacion_Clientes\Seleccione_Empresa.cs:línea 46
en System.Windows.Forms.Control.OnClick(EventArgs e)
en System.Windows.Forms.Button.OnClick(EventArgs e)
en System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
en System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
en System.Windows.Forms.Control.WndProc(Message& m)
en System.Windows.Forms.ButtonBase.WndProc(Message& m)
en System.Windows.Forms.Button.WndProc(Message& m)
en System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
en System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
en System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
en System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
en System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
en System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
en System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
en System.Windows.Forms.Application.Run(Form mainForm)
en Cotizacion_Clientes.Program.Main() en E:\PROYECTOS_VS2015\Cotizacion_Clientes\Cotizacion_Clientes\Program.cs:línea 19
en System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
en System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
en Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
en System.Threading.ThreadHelper.ThreadStart_Context(Object state)
en System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
en System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
en System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
en System.Threading.ThreadHelper.ThreadStart()
InnerException:
HResult=-2147467261
Message=El valor no puede ser nulo.
Nombre del parámetro: connection
ParamName=connection
Source=EntityFramework
StackTrace:
en System.Data.Entity.Utilities.Check.NotNull[T](T value, String parameterName)
en System.Data.Entity.Infrastructure.Interception.DbTransactionInterceptionContext.WithConnection(DbConnection connection)
en System.Data.Entity.Infrastructure.Interception.DbTransactionDispatcher.Commit(DbTransaction transaction, DbInterceptionContext interceptionContext)
en System.Data.Entity.Core.EntityClient.EntityTransaction.Commit()
InnerException:

What I have tried:

save Transaction
in the table was saved the transaction but this error is presented.