So it seems that for some reason (Older Dell laptop, ATI video, Windows 7 using generic drivers) the Windows system call to return the list of monitors is returning them to Racket in a different order (primary display monitor last) than expected (primary display monitor first). The code for get-all-screen-rects (in collects/mred/private/wx/win32/frame.rkt) assumes monitor 0 is the primary display monitor and is the first item in the list returned by EnumDisplayDevices. My tests show that at least sometimes the primary display monitor is not the first item in the list (also noted on SO at <a href="http://stackoverflow.com/questions/2600255/how-can-i-retrieve-monitor-information">http://stackoverflow.com/questions/2600255/how-can-i-retrieve-monitor-information</a>). An alternative solution to getting monitor information would be to use GetMonitorInfo passing a MONITORINFO or MONITORINFOEX structure for each of the values in the range 0 .. GetSystemMetrics (SM_CMONITORS) and used in Racket perhaps sorted by the monitor name returned in the szDevice field of the MONITORINFOEX structure. If Racket needs to designate monitor 0 as the primary monitor then get-all-screen-rects must enumerate the display monitors and then perform some processing to sort them so that the primary monitor is returned as the first item in the list. Cheers, Kieron.