Nice animation but...
it doesn't really go anywhere.
Your skills with Flash are pretty good but you're not using them to their full potential at the moment. Try to get a clear idea of what message you want to convey to your audience then set out to convey that.
This animation is quite a large file what what is essentially a very simple piece of storytelling. The dead files are returning from the grave, fine, but what do they do once they go back through the portal? What you've given us here is the first line of a story without anything more and it leaves the viewer thinking 'and then... Oh, that's it.'
Next time you make an animation try to see it from the audience's point of view. You've obviously worked very hard on the visuals but they don't achieve as much as that work should. This animation could convey what it has in half the time, which would then leave the remaining half to show what happens when they get to the other side... You could have them lumbering ominously through the dark, the lights come on and all the successful .swfs are holding a welcome back party for them, the zombie .swfs stand around looking embarassed, the end.
Something like that would have given the plot a feeling of resolution rather than leaving it open ended.
Actually, that's a pretty good punchline, I might use that in one of my animations...
Have fun and good luck with the next one!