Oldtown walls file has a destructible drawbridge. The troops tend to bunch up on it, and some of them have throwing weapons, which destroy the bridge. Missing bridge causes troops to drown, making assault impossible. Originally reported by Wascott on Moddb.
Screenshot.
[spoiler](https://i.imgur.com/ceMy9MW.jpg)[/spoiler]
Here is a fix, where drawbridge was replaced by it's non-destructible analogue.
https://www.dropbox.com/s/eglje24m9gybr9e/scn_town_22_walls.sco?dl=0
Cheers moose. I shall stick this in the next update.