Yep, the ladders need to be set to RenderMode "Solid" (iirc).
A couple of other observations:
The ladders are also MUCH thicker than you normally see. This may be deliberate, but most ladders are usually about 2 blocks deep.
Similarly, the boards between the cargo crates (across the top) feel a bit to thick when you're running about across the top of them.
I think one of your brushes is a bit small - where you enter the cargo bit on the side it doesn't quite meet the conveyer belt.
Nice job on the main room itself - it's good to see a room that isn't just a square block
How about making the conveyer belt work so you're pushed along it - maybe making that bit narrower so you can't jump on/off it when you're going round.
Anyway, just some observations/suggestions.
HTH
