problem with .PlotType = acWindow

hi

i am trying to create a routine to plot drawings... and for the first couple
of goes it seemed to work, but know for some reason, it falls over at the
..plottype = acwindow line... i've read the help files and it says that this
must be called after the .SetWindowToPlot (which it is) but i still get the
'invalid input'...

i've tried a few different things, first i set the page setup, to plot via
window (and therefore get the window option to be enabled in the autocad
plot dialog) then i stopped the routine at certain points to try and figure
out where my routine, disables the window option... .and for some bizzare
reason, when i call the .setwindowtoplot this sets the window option to be
disabled...
i've also tried using the example under the help, and this works fine

'code snippet
dLowerLeft(0) = 0
dLowerLeft(1) = 0
dUpperRight(0) = 841 'sDrawingSize(1)
dUpperRight(1) = 594 'sDrawingSize(2)

.PaperUnits = acMillimeters
.SetWindowToPlot dLowerLeft, dLowerLeft
.GetWindowToPlot dLowerLeft, dLowerLeft
.PlotType = acWindow
.UseStandardScale = False


any help would be great

cheers

mark