If you get this error, one reason might be an in-correct password, but in my case it was because I had upgraded my hard-disk. I had to re-enter my password to get it to connect again (un-check use stored credentials once). Looks like the HDD is used to generate some sort of key to store the password, or something like that, so you need to re-enter the password if you change your hard-disk.
AT&T Client could do with an more accurate error message though...
AT&T Client could do with an more accurate error message though...
