Since I upgraded to Snow Leopard (Mac OS X 10.6) I have been unable to download programmes using the BBC iPlayer Desktop. It worked fine before, but the upgrade killed it.
I tried uninstalling it, removing it using AppCleaner, uninstalling Adobe AIR, restarting etc etc, and eventually just gave up.
Today however I solved the problem!
I uninstalled iPlayer Desktop using AppCleaner, and then deleted the directory:
Where ~/ is your home directory.
I then went back to the iPlayer website, reinstalled iPlayer Desktop, and now all works fine!
I hope this helps someone else.