Try replacing your WAIT WINDOW command with

WAIT "" time .01

or (if in VFP8)

DOEVENTS FORCE

>This works, but I cannot have a wait window and display a white screen in the process of waiting for the user to press a key...
>
>

>set COLOR TO gr+/r, g/w+
>glfontname=_screen.fontname
>glfontsize=_screen.fontsize
>cOldbackcolor=_screen.backcolor
>coldforecolor=_screen.forecolor
>coldfillcolor=_screen.fillcolor
>clear
>@10,10 say "this is line 1"
>@12,10 say "this is line 2"
>#IF "VISUAL" $ UPPER(VERSION())
>	IF TYPE('printscr')="U"
>		PUBLIC printscr
>	ENDIF
>	ACTIVATE SCREEN
>	SAVE SCREEN TO printscr
>	_screen.lockscreen=.t.
>	_Screen.BackColor = RGB(255,255,255)
>	_Screen.ForeColor = RGB(0,0,0)		
>	_Screen.FillColor = RGB(255,255,255)	
>	_screen.refresh
>	ACTIVATE SCREEN
>#ENDIF
>
>*redraw screen as it was
>#IF 'VISUAL' $ UPPER(VERSION())
>
>	DECLARE Sleep IN Win32API;
>	  		INTEGER nMilliseconds
>	= Sleep(100) && Wait a 1/10th of a second.
>
>	ACTIVATE SCREEN
>
>	* TCH 7/10/2002 Added
>		
>	WITH _screen
>*		.lockscreen=.T.
>		.fontname=glFontName
>		.fontsize=glFontSize
>		.fontunderline=.f.
>		.fontbold=.f.
>		.BackColor = cOldbackcolor
>		.ForeColor = cOldforecolor
>		.FillColor = cOldfillcolor
>	ENDWITH
>
>	_SCREEN.lockscreen=.F.
>	
>	WAIT WINDOW "Press anykey..."
>
>	IF TYPE('printscr')!="U"
>		ACTIVATE SCREEN
>		RESTORE SCREEN FROM printscr
>	ENDIF
>
>	CLEAR DLLS "sleep"
>	
>
>#ENDIF
>
>RETURN
>