全部程序如下，目标是看一个遗传位点SNP与结局变量group（1=有病，0=没病）之间的关系.
已知exposure是暴露因素，SNP与exposure强相关。

reg exposure SNP
predict yhat, xb
logit group yhat, robust

rename yhat y2hold
rename exposure yhat
predict double res, residual
rename yhat exposure
rename y2hold yhat
replace res = res^2
summarize res

scalar realmse = r(mean)*r(N)/e(df_r)
matrix bmatrix = e(b)
matrix Vmatrix = e(V)
matrix Vmatrix = e(V) * realmse / e(rmse)^2
ereturn post bmatrix Vmatrix, noclear
ereturn display

运行程序之后，出错在下面一步：
. ereturn post bmatrix Vmatrix, noclear
estimates post: matrix has missing values
r(504);

求高手帮忙解答