Hi there
Did you enable Accessibility in the preferences?
Click Edit > Preferences > Project > Publish Settings and you should see a check box on the right side that is labeled: Enable Accessibility.
Note that I am not a huge Accessibility user so I have never seen it in actual use, but as I understand things, this option sort of "turns on the hailing channels" to enable communication between the flash object Captivate creates and the screen reader.
Cheers... Rick 