Game crash when entering Upper Prison

I try to enter the upper prison in merciless. The game crashes with this error written to the log file. Other files can not be loaded alos, but this is the only error written to the log file:

2013/12/17 11:28:37 10598583 115 [INFO Client 4224] Could not load room "Metadata/Terrain/Prison/Rooms/Unique/boss_cells_3a.arm", reason: "Metadata/Terrain/Prison/Rooms/Unique/boss_cells_3a.arm": Could not read y size