Some of my visitors are on outdated machines with old versions of Flash. My FLA consists of nothing more than a few lines of ActionScript that create a SharedObject.

I want to ensure my SWF executes for them. Is there any reason I should NOT select an older version of Flash Player and ActionScript when publishing the file?

• actionscript
• flash
• shared-objects

1. You should try and see if it works.
2. Show the "few" lines of code? It's easier to tell if anything will break if you know what may break.
3. Considering non-code-related changes: CFF fonts will not be available to you in the old version, I believe, couple of line styles, too. No shaders, obviously. The overall display list performance will be a bit slower - that's about it.

People using old version of Flash player, however, are putting themselves in danger of all kinds of exploits and other malware that can target older versions of Flash player, so at least for that reason you could encourage them to update.

If all you are using is a SharedObject, you can target Flash 9, but not less.

As for educating your users to upgrade, I wouldn't bother with that. To convince them of anything, you'd have to at least write a whole page detailing the possible exploits and so on, and that's probably not the purpose of your website.