Not sure what you tried to attach or how you did it, but it doesn't work the way you did. See how to attach files at the top of the page.
However, I suspect the issue isn't about references. It may be caused by user action. If you can use the same pc and do what you normally do and see what happens that may add a clue. That message is often caused when you open a form or report by using a procedure and something causes that form to close. When code execution returns to the calling procedure, it reports that the form isn't open because you need to know that for sure.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.