Thread:Extension talk:AJAXPoll/Users - Already voted, despite not voting.

I'm currently using the Extension on our Internal MediaWiki Server, where I created a poll upon which everybody in the internal Network should vote on without beeing needed to Log In. For some it works ok, for others it says they already voted, despite this not being the case and everybody having a unique internal IP. What can I do? Can I maybe switch to cookies?