Looks like I have the same problem (Windows 7 64, Visionaire 4RC, build 1165). When I start dialog just after the game starts and choose any dialog option, the game crashes. However, when I wander around the scene first, click some objects and then starts the dialog, the mouse pointer dissapears and I can't choose anything.
There aren't any errors in the log file, except "Abnormal program termination".
I may have ommitted something, I'm a beginner at Visionaire.
Thanks for help.