In April 2008, Adobe imposed new security restrictions on socket connections made by Flash Player. Starting with Flash Player 126.96.36.199, all socket connections made to a server require authorization via a socket policy file.
For a general introduction to the issue of mandatory socket policy files, see Unity technote 00005.
For full, gory coverage of the security changes made in Flash Player 188.8.131.52, including their motivation and required action, see the following resources:
Think you've found a legitimate bug in Flash Player? You now have a public place to report it: Adobe's new bug-tracking database for Flash Player.
Beyond its usefulness as a feedback channel for developers, the bugbase should be a nice resource to check when researching known Flash Player issues and their workarounds. Bugbase users can also voice support for fixes to existing bugs, which will help Adobe prioritize their engineering efforts based on community feedback.