毕业论文跑下面code，一直出错，上网查了两天（中英文网站查遍!）都没法解决啊TAT心力交瘁，求高手解答!
数据结构是这样的，3-level 重复测量数据
level_1 (participants, n=5000+) is nested within level_2 (school, n=200+), which is nested within level_3 (countries, n=12).

Study objective:
1. random effect for level_1 and level_2;
2. Fixed effect for Level_3, and test the exposure*level_3 interaction.

proc glimmix data=;
class  level_1 level_2  level_3  covariates;
model outcome = exposure  level_3 exposure*level_3 covariates;
random intercept / subject = level_2;
random intercept / subject = level_1 (level_2);
run;


SAS 一直报错：The SAS System stopped processing this step because of insufficient memory.


我的问题如下：

1. 如何解决SAS报错问题啊？

2. 我的SAS codes对吗？level_3虽也有nested, 但是我只放在了Model statement那里。

3. 我换过PROC MIXED，也是一样的memory error，然后网上说换成HPMIXED 可以，我试了，程序跑起来了！但是只能出type 3 analysis fixed effect的结果，但是没有parameter estimates啊…求问高手解决这个问题!