It's a known bug. Download last sp from Microsoft.
http://www.microsoft.com/downloads/release.asp?releaseid=35414

>We support a networkable program that is compiled in VFP 7.0. Our users have sporadically reported problems when working with multiple applications that when they are working in our application and then try to click on the taskbar to maximize another application they can't maximize it until they minimize our program. Has anyone else seen this and been able to correct it?