Is this possibly because there's too much for it to handle?
I've come across a situation before with a thirty second clip not rendering out fully because it was just too heavy going on the computer, but if I asked it to only do 5 or 10 seconds it would be OK. But this is just my work around and not any kind of solution.
Maybe just try rendering out small parts of it at a time if it's just for working with/ preview purposes?
Is this a change in behavior? What kind of wav file? What are your render settings? What is the length of your work area? Are you new to AE?
There's not enough information about your problem to do anything but make wild guesses.
Try adding your composition to the render cue. Set the length of the comp to entire composition in the Render Settings. In the Output Module try using QuickTime and setting the codec to JPEG and quality to 90%. Check enable audio and leave the settings at the default 48KHz 16 bit... Let us know if that works. If not try and provide more information about your project.
I sent the project directly to Media Encoder instead of using the built in renderer in AE and that worked perfectly with output of both .mp4 and .mov, so I'll just stick with that as my rendering solution.