Where is the request coming from? A web site your on or something else?
If you use a browser other than IE or Edge (or Chrome) it's possible the update is for that browser, but the update would only display once every 7 days upon system log in. If you're getting update notifications more often than that it's possible it's not from Flash Player. The next time you get a notification please take a screenshot and post it here (see The specified item was not found.). We can view it and determine if it's a valid Flash Player notification or not.