Thats an error that happens when you have too many brushes ( the steps ) intersecting a single face ( the ladder rail ). Cut the ladder rails into smaller sections ( say 5 steaps each ) to get rid of this problem.
If your ladder isn't crazy long, your problem could also be that one or more of the rungs are conflicting, i.e. inside eachother. Also, select all the rungs and rails and press 'ctrl+g' to snap them to the grid. You can get the same yellow/gray/black stuff from unaligned/snapped brushes.
