group policy object does not apply

hi,

i have almost 500 users on my active directory, all associated with one group policy object. in that gpo, i have specified some settings, like change desktop, restricted access on desktop, as they cannot change wallpaper, and a network drive is mapped. however, for some users, the gpo is applied, but for others, that gpo does not apply. they are not restricted users when logging on computers, and that network drive also is not mapped.

any advice plz?

thanks.