I ran the below code with no problems.  Maybe try a try a loop with WinActive that calls the next window until successful.   #include <IE.au3>
Local $dropTask = _IECreate("www.google.com/")
Local $focusSupportPage  = _IECreate("www.msn.com/")
WinSetState($dropTask.HWND,"", @SW_Minimize)
WinSetState($focusSupportPage.HWND,"", @SW_Minimize)
While 1
    While Not(WinGetState($dropTask.HWND) = 47)
        WinSetState($dropTask.HWND,"", @SW_Maximize)
        WinActivate($dropTask)
    WEnd
    Send("{f11}"); full screen
    Sleep(10000)
    Send("{f11}"); full screen
    WinSetState($dropTask.HWND,"", @SW_Minimize)
    While Not(WinGetState($focusSupportPage.HWND) = 47)
        WinSetState($focusSupportPage.HWND,"", @SW_Maximize)
        WinActivate($focusSupportPage)
    WEnd
    Send("{f11}"); full screen
    Sleep(10000)
    Send("{f11}"); full screen
    WinSetState($focusSupportPage.HWND,"", @SW_Minimize)
WEnd