We've made modifications to OpenCascade. You can download the latest version of the source code from http://www.navisworks.com/files/OpenCascade.zip.
See the file NavisWorksModifications.txt for a list of all the files we've changed.
I tried to email you to the address given in this thread (http://www.opencascade.org/org/forum/thread_5607/) but the email bounced. Who should I email in future?