I am getting this error when I try to save a record:

System.InvalidOperationException was unhandled by user code
HResult=-2146233079
Message=This SqlTransaction has completed; it is no longer usable.
Source=System.Data
StackTrace:
at System.Data.SqlClient.SqlTransaction.ZombieCheck()
at System.Data.SqlClient.SqlTransaction.Rollback()
at OakLeaf.MM.Main.Data.mmDataAccessBase.TransactionRollback(IDbTransaction transaction, IDbConnection connection)
at OakLeaf.MM.Main.Data.mmDataAccessSql.TransactionRollback()
at OakLeaf.MM.Main.Business.mmBusinessObject.TransactionRollback(String databaseKey)
at OakLeaf.MM.Main.Business.mmBusinessObjectGeneric`1.TransactionRollback(String databaseKey)
at OakLeaf.MM.Main.Business.mmBusinessObject.TransactionRollback()
at OakLeaf.MM.Main.Business.mmBusinessObjectGeneric`1.SaveEntityList(mmBindingList`1 entityList)
at OakLeaf.MM.Main.Business.mmBusinessObjectGeneric`1.SaveEntityList()
at OakLeaf.MM.Main.WPF.mmBusinessUIHelper.SaveEntityList(ImmBusinessContainer container, mmBusinessObject businessObject)
at OakLeaf.MM.Main.WPF.mmBusinessWindow.SaveEntityList(mmBusinessObject businessObject)
at OakLeaf.MM.Main.WPF.mmButtonHelper.SaveHandler(Button button, Boolean saveAll, ItemsControl itemsControl, String bindingSource, mmBusinessObject& businessObject)
at OakLeaf.MM.Main.WPF.mmButtonSave.mmButtonSave_Click(Object sender, RoutedEventArgs e)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.Controls.Button.OnClick()
at System.Windows.Controls.Primitives.ButtonBase.OnMouseLeftButtonUp(MouseButtonEventArgs e)
at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.ReRaiseEventAs(DependencyObject sender, RoutedEventArgs args, RoutedEvent newEvent)
at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args)
at System.Windows.Input.InputManager.ProcessStagingArea()
at System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
at System.Windows.Interop.HwndMouseInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawMouseActions actions, Int32 x, Int32 y, Int32 wheel)
at System.Windows.Interop.HwndMouseInputProvider.FilterMessage(IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at System.Windows.Interop.HwndSource.InputFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
InnerException:

I have no idea where to start on this one.

Any suggestions as to what could be the cause?