What version of AppGameKit are you using?
Something that has popped up for a while is that assigning GetDeviceWidth/Height to a variable, in Tier 1, and using that variable doesn't always work.
FUNCTION InitResolution()
SetOrientationAllowed( 0, 0, 1, 0 )
SetDisplayAspect(GetDeviceWidth()/GetDeviceHeight())
ENDFUNCTION
You could also try this (maybe it is an ordering thing):
FUNCTION InitResolution()
SetDisplayAspect(GetDeviceWidth()/GetDeviceHeight())
SetOrientationAllowed( 0, 0, 1, 0 )
ENDFUNCTION
Cheers,
Ancient Lady
AGK Community Tester and AppGameKit Master