hi,
Only animations on the main timeline are playable in AE, animations nested into moviclips won’t. I know it can be a pain but there are some options though :
1/ ask the author to change his FLA and make his animations, if he can, in the main timeline.
2/ decompile the swf with sothink decompiler (for example there are others) and then edit the animations yourself, but this means you know what you’re doing.
3/ ask the author to export his animation in mov or avi and then import the movie in AE. You can convert the swf directely into a mov or avi too using some free software, just google for it.
hope it helps, best luck
dogimo