There are updates between major Vizard versions (i.e. Vizard 3 to 4, and Vizard 4 to 5), that could potentially break scripts. We have upgrade guides in both the Vizard 4 and 5 Help that document these changes. The following is a link to the Vizard 5 upgrade guide from our online documentation:
http://docs.worldviz.com/vizard/#Upgrade_guide.htm