I was having this exact same issue described here but I have Xfinity:
I tried removing Xfinity to fix the issue but got the problem described here:
I had two Xfinity accounts, one for internet and the other for TV. I made sure and turned off auto authentication.
Now when I go and try to log in, I get:
Cable provider authentication failed
I've read some places to change the Comcast password and I have a couple of times. I'm getting the same error on different computers on different networks.