New-error-message-when-copying-signals-from-metastrategy

I have a meta strategy with five substrats. Today it generated 16 signals, but I am getting an error message never seen before when I try to COPY SIGNALS (using right click). Usually I only have 6-10 signals, but this morning there are 16 signals, if that makes a difference. This happened in build 154, so I upgraded to build 157 and the same thing happens. This is the message (from 157):

System.NullReferenceException: Object reference not set to an instance of an object.
at WealthLab.WPF.ucSignals.StartInvocation(Object asset, RoutedEventArgs pred)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.Controls.MenuItem.InvokeClickAfterRender(Object arg)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)