'System.Reflection.TargetInvocationException' occurred in PresentationFramework.dll

Question

The event is probably raised before the elements are fully loaded or the references are still unset, hence the exceptions. Try only setting properties if the reference is not null and IsLoaded is true.

To diagnose this issue, place the line of code causing the TargetInvocationException inside the try block.

To troubleshoot this type of error, get the inner exception. It could be due to a number of different issues.

try
{
    // code causing TargetInvocationException
}
catch (Exception e)
{
    if (e.InnerException != null)
    {
    string err = e.InnerException.Message;
    }
}