LAN91C111 revision C with LWIP

For a project we made a "copy" of the Cyclone II 2c35 board with the only significant difference that the original LAN91C111 rev. B on the board is replaced with a LAN91C111 rev. C

At this moment the LWIP stack does not function and when accessing the registers of the LAN91C111 (Base address + offset 0x300) no data is read.

Does anyone have suggestions regarding this problem.