in 13w22a when ever i go to a certain area of my adventure map i get a crash

Put the summary of the bug you're having here

in 13w22a when ever i go to a certain area of my adventure map (nivenska nights (google it great map , well i would say that ) , working on version 5 currently , we have over 22k downloads, anyway back on track) i get a crash , trying to implement horses into this version before the 1.6 release so it is ready when it does come out, although its being a bit tricky

What I expected to happen was...:
the area would load , drawven ruins

What actually happened was...:
it damn crashed

Steps to Reproduce:
1. go to the area and it crashes