In the most recent version of Flash released in mid April, Adobe has changed the rules on how .SWF files are allowed to talk back to the server. The main motivation appears to be the old model did not give the host enough control over the abilities an .SWF aplication. The new model allows for tighter security and the improved security is there by default.

Side-effects being that if you used to rely on:
- doing HTTP requests (with loadVars for example).
- having .SWF-files load other .SWF-files.
- loading data using for example XML-files or AMF-PHP or SWX.