Hi Israel, I was having the same problems with Vegas 8.0C and Audition 1.5 (it’s old, but it works). The workaround I found was to split the audio into smaller bits. If you make sure that the audio is not locked to the video, select a point in the audio timeline and hit ‘s’ which will ‘split’ the audio. Then pick a place a little farther down (maybe under 5 minutes) and do the same thing. Now you should be able to “open copy in audio editor” with no problems. Just make sure that Vegas has not inserted fade points and you will never hear the split.
Let me know if that works for you. If not, you may need to experiment with different audio lengths.