I'm doing research on automatic difficulty assessment of puzzle games. For this research, we need data about the difficulty of puzzles as perceived by real players, and we are currently performing a user study. One of my students has re-implemented three popular puzzle games. We need people to play the games, and for each level estimate its difficulty.
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Thanks. The same problem has been reported by others using IE; it seems to be a cookie issue. We are working on it. Meanwhile, using a different browser should also solve (or rather circumvent) the problem.