SAS proc mixed empirical standard errors

Question

I'm fitting a 3 level mixed model and trying to compute empirical rather than model-based standard errors for the fixed effects. When specifying the empirical option in PROC MIXED, I get a warning that I only have one effective subject. There are a lot of subjects in the data set, so i'm unsure what the problem is. Here is my code.

PROC MIXED DATA = EngScores METHOD = ML empirical; 
CLASS id t region sex;
MODEL achieveEng = edu age sex time time*time / solution; 
REPEATED t/type=un subject=id;   
RANDOM intercept / subject=region;   
run;