Contrasts for 3-way ANOVA in SAS

#1
Hi,
I am trying to estimate the simple effects for a three-way interaction.
I have tried with this syntax

PROC GLM data=study_3;
class extr int des_med;
model att=extr|int|des_med;
LSMEANS extr|int|des_med;
contrast 'main extr' extr -1 1;
contrast 'extr in loint lodes' extr 1 -1 extr*int*des_med 1 0 0 0 -1 0 0 0;
contrast 'extr in loint hides' extr 1 -1 extr*int*des_med 0 1 0 0 0 -1 0 0;
contrast 'extr in hiint lodes' extr 1 -1 extr*int*des_med 0 0 1 0 0 0 -1 0;
contrast 'extr in hiint hides' extr 1 -1 extr*int*des_med 0 0 0 1 0 0 0 -1;
run; quit;

But the log says that these contrasts are not estimable.
How can I do?
I want to see how the interaction between extr and int changes across the levels of des_med.

Help is extremely welcome :)thanks
violet