Recently. our Dell desktop and Dell laptop, both with Win7, lost the ability to share files over our Homegroup. When I run the troubleshooter, it reports that the "administrator has disabled Teredo locally." This is confirmed when I view Device Manager. Delving further, I am told that I have to enable IPv6 in order for it to operate. Problem is that when I go to Network properties, IPv6 is checked as being enabled. As far as I can tell it's all running as it should.
As a side note, I remember when we first loaded Win7, I had to go to the registry string for the IPv6 and change 2-3 characters on the end of the string to get it to work. Can't find that forum reference now, so I'm wondering if someone might be able to help.