I just started having the same problem as well. I have Vegas 9.0 & it’s worked great since i got it about a year ago… Then just today it started only rendering audio.
As they’ve said Final Cut & AE are completely different programs. But if you need to do both & you’re looking to save a few bucks, you could always buy Sony Vegas Pro & AE. Then use ’em together (vegas for editing & AE for compositing).