Flex messaging (Flex Data Services, FDS, FDS2, now called LiveCycle) requires that the display-name entry be in the web.xml (for sure in JBoss, I assume in other Java servers).  Otherwise you will get errors similar to these:

08:04:06,018 ERROR Servlet threw load() exception
java.lang.NullPointerException
at flex.management.BaseControl.getObjectName(BaseControl.java:287)
[…]

This one kind of bugs me.  If you don’t create an event handler on the flex/flash NetStream object for the AsyncErrorEvent and you call the NetStream.play function you will get the following errors. Well, you will see it in the flash debug player.
ERRORS:
Error #2044: Unhandled AsyncErrorEvent:. text=Error #2095: flash.net.NetStream was unable to invoke callback onMetaData. error=ReferenceError: […]

Flex2 with FMS2
OK, this one caused me to waste a bit of time so here I’m going to describe the problem in detail.  Hopefully it will save someone else the trouble I had.  Basically Flex 2 defaults to AMF3 and Flash Media Server 2 will only support AMF0.
On the FMS server side the application was […]