Not sure about what your aiming to do, but, to stack KZ, you should use the SUBGROUP options. The following modification will suffice.
proc gchart data=work.GrundlageGrafik;
format datum ddmmyyp10.;
vbar datum / sumvar = stapel
group = gruppe
subgroup = KZ /* datum */
legend = legend1
patternid = subgroup sum
raxis = axis1 maxis = axis2 gaxis = axis3;
axis1 label=none minor=none;
axis2 label=none value=(tick=1 '' tick=2 '');
axis3 label=none order=('Bis 2 Tage' '3-5 Tage' '6-8 Tage' 'Aelter 8 Tage');
run;
GROUP, will combine categories and SUBGROUP will stack values.
Is this what you want?
Check the online documentation for SAS Graph in particular for the gchart procedure:
http://support.sas.com/documentation/onlinedoc/graph/index.html
And give a look at the sample gallery:
http://support.sas.com/sassamples/graphgallery/index.html
Cheers from Portugal.
Daniel Santos @
www.cgd.pt