I have reset my state (MA) website and am trying to delete national events that we do not plan to run.  I get the following error message:

This event has a test created for it already. You cannot delete the event until either the test is removed or cloned.

How do I resolve this issue so that I can delete this event?

Each year the event arrangements are different. If you retain last year tests, they wouldn't match. You should export the tests to PDFs then delete them to get ready for the new season.