I've been experiencing an intermittent issue in Flash CS5 where sometimes I can't nudge anything using the subselect tool. Sometimes I can, but most of the time I can't, and I don't know why.
I can still click-and-drag points (or multiple points/paths), but I can't nudge them using the keyboard.
My guess is the item is grouped and your are editing inside the group? For some reason in that case you can't nudge the points in that manner.
Break the group apart and try it again. Sorry that is the only answer I know.
Glad I could help!
There are still some really big old bugs in Flash that have been around since at least Flash 5 (I think CS6 is actually Flash 12?).
There are so many ****** problems with it that Adobe haven't fixed - they've just piled more features on top of them and hoped nobody would notice.