Are you on the original software that came with the phone or the dl mode version? I had the same problem but I was on the dl mode with root so I ended up doing the dl mode again and put my phone to stock v3, then I checked for update without getting root or setting anything up on the phone, and it installed and updated to v4 fine. No root this way but I don't really need it right now. So far the phone is running fine, but I will need to test it over the next couple of weeks to know for sure.

 

I'm having the same problem. Unlike you, I am rooted. But I am running the original stock rom. I tried twice, and took it as a sign that I would be unhappy without root.

 

I believe you can use the lg flash tool with https://www.lg.com/global/support/opensource/opensourceList?types=ALL&search=Volt to directly flash the updated rom as a last resort.

 

Use the prerooted ROM on here to update.