It is unfortunate that Adobe have made this change (and even more unfortunate that their own workaround instructions were initially inaccurate, being that their own web page buttons do not work in all browsers) but there is nothing that can be done within SimpleViewer to change this. It is not possible to change a user's Flash security settings from within a SimpleViewer gallery.
Agreed, it is an inconvenience to have to make a change to your Flash security settings (especially when you do not know what the problem is) but adding your Documents folder (or whatever folder you choose to store your galleries in) to the list of 'Trusted Locations' is a one-time change which will allow you to continue viewing SimpleViewer galleries locally as you have done in the past.
I have notified the developers with a suggestion to add this issue as a FAQ. This should make it easier for other users to find the information.
What long-term solution do you have?
Unfortunately, there is no denying that Flash is a dying format.
Adobe have just made it more difficult for users to view Flash applications locally. (Link.)
Flickr have recently taken the decision to deny all Flash applications access to Flickr images via their API. (Link.)
Chrome will begin to block Flash from version 53. (Link.)
Edge is also moving in the same direction. (Link.)
In 2017, Firefox will require click-to-activate approval from users before a website activates the Flash plugin for any content. (Link.)
If you are looking for a long-term solution, then I would recommend migrating from a Flash gallery to an HTML 5 gallery.
You might like to take a look at Juicebox, an HTML 5 gallery which does not use or rely on Adobe Flash Player at all.
It is possible to convert a SimpleViewer gallery to a Juicebox gallery by following the instructions here.
Please see this SimpleViewer blog entry for information on why we created Juicebox, the differences between SimpleViewer and Juicebox and for details of a discount off Juicebox-Pro for existing SimpleViewer-Pro users. (Please note that the blog entry was written over 4 years ago, long before any of the developments regarding Flash which I have linked to above.)
Please note that due to certain browser security restrictions, it is not possible to view Juicebox galleries locally in all browsers.
FAQ: When I view my gallery locally, I see the message "Juicebox can not display locally in this browser". Why?
This does not affect the live preview in JuiceboxBuilder (the desktop application to build and edit Juicebox galleries) which has no problem displaying galleries locally. Also, it should be noted that this issue affects local viewing only; there is no such problem viewing galleries once they have been uploaded to a web server.
Like the recent Adobe Flash issue, it is not possible to circumvent these local browser security settings from within a Juicebox gallery. However, being HTML 5 (and not being reliant on a third-party plugin), Juicebox galleries should still be much more future proof than any Flash gallery (and no third-parties should be able to pull the rug out from under our feet).
SimpleViewer Support Team