I could not reproduce the nil-value-index error, and got successfully started to Trollshaws. However, there was no water around, and I immediately changed the mode to 16x16 graphical. After about 40 minutes (visiting Bree in the meantime, no problems with water tiles in the Wilderness), I tried to switch to 32x32 near water and got greyscale squares instead of tiles, and trying to switch to any other mode did not help.
[DISPLAY MODE] 32x32 GFX
C Map size 18:14 :: 252
[MINIMAP MODE] 1
[MINIMAP MODE] disabled
Loading tile tactical_enemy.png
Loading tile tactical_friend.png
87 ticks in 11.722 seconds = 7.42194 TPS
280 frames in 10.014 seconds = 27.9609 FPS
If fancy things only work with 32x32, is it possible to have 16x16 as the default mode?
EDIT: anyway, I am waiting for beta6, as save/load is broken in beta5.