My video editing consists of cutting an hour-long program into 5-8 parts that need to be exported individually. So what I've been doing is copying and cutting all the parts except one, exporting that one part as an MP4 file, then undoing the cut and doing it again but for a part I have yet to export. So for a 5 part project I do that 5 times, so there are 5 exports. When I first started this a few months ago, each export would be perfect. Now, as soon as I do the second export, it appears to work but when I go play the video the audio didn't come with the export. So I have to close Adobe and reopen it, then it will work. But now it's to the point where I can do one export, then I need to close out of Adobe entirely, re-launch it, then I can export one more file. So now to export 5 parts I have to close and re-launch Adobe 5 times. It's unbearable. I'm using my work computer which is running Windows 7. 64-bit.
There is pretty likely a simpler way to do what you're doing. Have you tried just loading the whole project on your timeline and then using the Work Area Bar to designate and output one segment at a time?
That said, which version of the program are you using?
What model of camcorder is your video coming from and what format and resolution is it?
Which Share settings are you using to output your MP4s?
What do you mean when you say "I first started this a few months ago, each export would be perfect." Are you saying that you've already done all of your exports but now you're doing them again? Did something change between then and now?