Ok, I recreated the problem on windows by turning off cookies. I was getting the cookie id without setting a value, but for whatever reason some users aren't accepting cookies? Anyways, I changed where the key is getting generated, and I think it should work for you now.
The key here is that a lot of users might enable settings to make themselves anonymous on the internet, many of those settings, default or not, will render themselves unable to vote on TWC, because in order to weed out bots, they specifically have to "not" be anonymous, twc doesn't need to know "who" they are, but it has to know they're a computer on the internet, and that they're the same computer shown the first votepage, the first click, and the 2nd click, if the site detects anywhere that the computer is different, not the same, or anonymous at any of those 3 steps, it prevents the vote from counting.
Having said that, hopefully this fixes the issue, let me know.
Richard M.
Grimfang"Whisper"Xaeraes