I have the exact same issue. I transferred two movies from my Panasonic VHS player and the sound worked great. Now the audio stopped working, I have been trying for DAYS now to get it to work again. I KNOW the sound is making it into my computer because I can see the signal in the preferences sound window. PLUS, I connected the VHS to a TV and the audio totally works. So there is no problem with the VHS unit, the tape, cables or the hardware. It has to be the ROXIO software.
I have read A TON of complaints about the Roxio easy VHS to DVD for Mac software concerning the audio suddenly not working. WHAT IS GOING ON ROXIO???????
So yeah, this really sucks and everyone is also blogging about how bad their customer service is so now is the time for the company to listen to its customer base. I am very frustrated and upset since I can't afford another $80 and I really need this footage for a deadline I'm on.
Unless Roxio or someone can solve these audio issues, many of us will not be purchasing any products in the future.
Thank you in advance for any kind soul who has figured out a work around. I tried many solutions I found online like plugging and un-plugging the hardware in at various stages, moving the contents of the quicktime folder to a new folder on the desktop, etc, etc, etc,.