I share one of my development machines with another flash developer and have run into a problem whereby the debug flash player was only available to the user who installed it. Trying to set more generous permissions on the plug-in didn’t work. So I simply changed the name of the plug-in by prefixing it with the installing users name then reinstalled it as second user. This leaves you with multiple instances of the flash player in Library/Internet Plug-Ins but as each user only has permission to use the player they installed no confusion arises. The most recent debug player can be found here. An archive of debug players can be found here.