If you encounter Action Script error #2148 you should consider two things:

First of all, it may be a crossdomain policy issue

It may also be a Flash security problem. Read the following links to get some useful technical background information:

Curtis J. Morley Flash/Flex Blog

Xcelsius 2008 Best Practice Guide (Page 11)

Macromedia Flashplayer Settings Manager

For those of you, who don't like reading background information and prefer try and error, set the XML-Source directory as trusted site in the Flash Settings Manager below or hit Adobe Flash Settings Manager.