Hi cris53,
The Count film contains, arguably, the hardest puzzles in the game. The trick to opening that door with the II+III is to go into the room with the three puzzles in it. Puzzle I unlocks puzzle II by setting the tiles to "II". Solve puzzle II, then go back to puzzle I and unlock puzzle III by setting the tiles to "III". Solve puzzle III, then go back to puzzle I and set the tiles to "IV" to allow you to leave the room. Now that locked door should be open!
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