Hi,
I suspect that Maze Creator STD was not installed properly. From your Ver 3.x it seems like it is the STD shareware version not the free version. VISTA has got its problems and installation of new programs is one issue.
Try to uninstalled the application, download the very latest as that should help the installation process with VISTA. Save the setup.exe to your desktop and make sure you right-click on it and "Install as Administrator". This will allow it the proper access to install correctly.
If this doesn't fix the issue, were you using Circular mazes prior to trying to make a "Box" style?
Regards,
Maze Creator