Flash Player is only allowed to load certain assets from an external server. Needless to say this can be inconvenient when you are testing locally, as you will surely be peppered with Security Sandbox Violation errors. To get around this limitation, you can set up a trust file. The trust file tells Flash not to concern itself with the security of swfs running in the specified folder on your hard drive.

We’ve had to do this for ages, but I still run across people who have never heard about it.

There’s actually a GUI that looks like it ought to be able to do this for you here in Adobe’s strange little web-based local settings manager thingy:

http://www.macromedia.com/support/documentation/en/flashplayer/help/settings_manager04.html

However, I have found it doesn’t like to save my settings. You might try it first to see if it saves you the trouble of going through the steps below.

Here’s how you make a trust file manually (these instructions are for the Mac):

Find the folder at the following path:

~/Library/Preferences/Macromedia/Flash Player/#Security/FlashPlayerTrust

If any folder in that path doesn’t exist you can create it. Using a plain text editor, like TextMate, make a new file. Inside that file, write the path for the trust file. For example:

/Users/username/Documents/Projects/

Then save it with an arbitrary name like “MyTrustFile.cfg” The important part, obviously, is the .cfg extension.

I have also seen developers who just set their trust file to trust everything on their hard drive. That’s really asking for trouble. Presumably, all swfs are not automatically trusted for a reason!