Post hoc turkey test

#1
Hi all,
I am quite new to SPSS.
My soil analysis includes eight treatments at three different stages for various parameters (total organic carbon, soil enzymes, nutritional status, poulation dynamics)
If i am performing two way ANOVA for singe parameter (e.g: soil enzyme), followed by post hoc test, the error i could face is post hoc tests for treatements coud not be performed because the error term has zero degrees of freedom.
I do not know, what is the blunder i am doing.
kindly do help me out
 
#2
mmmm, turkey tests. my diagnosis is that you do not have any repetition in some or all cells of the experiment?