Almost always if it works on your local machine and not on the server, it's a pathing issue. Did you test the .swf on your local machine with the .swf and the .xml in the same folder? Is the Web page in that same folder or a different folder? As soon as that .swf is placed on a Web page outside the folder it's in, you are in effect removing it from that folder, which also alters the path back to the .xml.
Can you download the .xml file by directly typing the address in the browser (the absolute path)? It may not display properly but it should load at least a portion of that file in the browser. If you get a "File not found", then either the file is missing or it's someplace where it's not supposed to be.
I'd check out all possible pathing issues before worrying about security classes.
Best wishes,
EfV