Glitch - variable speed, even though a fixed speed has been programmed

[EKF]

Hi
I have Vizard 3 and I'm using a brick wall maze which a programing friend helped to write. People walk through the maze (first person perspective) using the keyboard arrow keys.
This worked fine on my old laptop, but I have just moved Vizard to a new laptop, and the walking speed is now really variable despite it being programmed at a fixed speed. I've uninstalled the antivirus software on the advice of a colleague, but this still doesn't help. I also created .exe files rather than loading directly, and I have the same problem.
Any advice greatly appreciated.
Thanks