Are they all running the same version/service pack of Windows?

>We have some clients that are using our application written in VFP 9 SP2.
>
>They were telling us that a mouse click wouldn't open the menu pad but they could use the Alt+Hotkey to open the pads. After connecting with their workstations we found that if you hold the mouse button down, the menu pad will finally open. Has anyone else seen this? At first I thought it might be a video driver problem but their workstations are from different manufacturers with different video cards.