What does "The URL is not in the Proxy's whitelist" mean

Question :What does "The URL is not in the Proxy's whitelist" mean?
Answer :The whitelist is a security feature in Flex that requires you to define explicitly which URLs a data
service call can access.
You set this by editing the following file: ...\[flexroot]\WEB-INF\flex\flex-config.xml
There are three sections, one each for WebService, HTTPService, and RemoteObject. Be sure you
edit the correct section! Each has a subsection which contains nodes. To enable a URL for access by
a Flex dataService call, enter that URL between the tags.
For development phase only, you can allow global access with the wildcard rows. The flex-config
file is heavily commented. Open it up and you will see more detailed instructions there.