Do you have an AOL account? I seem to recall some years past where an AOL account was problematic due to the way AOL shifted IP addresses or something like that.
Silly solution -- but is there a public library or other place you could try voting from? That would tell you whether it was your username or your IP address that was causing the problem.
I think my best bet would be a libray, but I resent having to pay for the net on top of my bills! Suppose it's the way it goes though, I have the day off tomorrow so I'll go then.