is the build linked together? Sometime people do modify linked builds without unlinking and then face strange bugs.
If is it linked unlink it, modify the path cut of the tubus manually, wait some while (or fire backup command on the console) and link it back.
Sometime can help tickle "disable colisions" in the debug tab of the region/estate window. Especially when you are using hollows for the doors. Not sure if it will work for you but anyway it improves performance
Another problem is "too high step". Eg in SL you can have higher step that here. Fix is easy, add an transparent "bridge" to allow avie pass the problematic spot.