Photoshop layer masks are not the same thing as an AE mask; they’re more like Alpha channels.
It works for me. When I import it into AE I get the trasparency. If, for some reason it’s not working for you then I would just merge the layer with its mask and save it into a seperate file for importing into AE.
Unless you want to have a changeable mask in AE, in which case… hang on, I’ll think of it.
Ah, I’ve got it: On a PC ctrl-click on your layer in the layer pallette (I’m not sure the mac keys, you’ll have to figure it out yourself if you’re using one) you should see those lovely little marching ants around your layer. Then go to the paths tab (probably on your layers pallette) click that little arrow on it. Select Make Work Path. You can then double-click it to make it a proper path. You can copy it and paste it into After Effects then and apply it to your layer.
I hope that made sense and didn’t confuse you.
– The Great Szalam
(The ‘Great’ stands for ‘Not So Great)
No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.