用nlximed运行多水平零膨胀负二项模型，用多水平logistic、多水平负二项做logit和负二项部分初始值，得出结果好多的".",日志有错误报告：WARNING: The final Hessian matrix is not positive definite, and therefore the estimated covariance matrix is not full rank and may be unreliable. The variance of some parameter estimates  is zero or some parameters are linearly related to other parameters. 该怎么修改程序？是哪里出的问题？
程序如下：
proc nlmixed data=sasuser.c7;/*多水平零膨胀负二项(logistic yn)*/

parms  A0=-0.2285 Asex=-0.5112 Aage=-0.00767 aedu=0.07857  aq32=0.2301 avolun1=-0.2291 adrink=-0.4512
ac10new=0.2190 ac11new=-0.2265 apress=-0.1642
B0=-0.09054 bsex=-0.4259 bage=-0.00888 bvolun1=-0.2152 bc10new=0.1656 bc11new=-0.2021
v_u1=-107E-14,cov_u12=1,v_u2=0.2758 k=1.3513;
s1=A0+Asex*sex+Aage*age++Aedu*edu+aq32*q32+avolun1*volun1+adrink*drink+ac10new*c10new+ac11new*c11new+apress*press+u1;
p=1/(1+exp(-s1));
s2=B0+Bsex*sex+Bage*age+Bvolun1*volun1+Bc10new*c10new+Bc11new*c11new+u2;
lambda=exp(s2);
pdf=gamma(n+1/k)/(gamma(n+1)*(gamma(1/k)))*(((k*lambda)**n)/(1+k*lambda)**(n+1/k));
if n=0 then pdf=p+(1-p)*pdf;
else pdf=(1-p)*pdf;

if pdf>1e-8 then ll=log(pdf);
else ll=-1e20;

model n~general(ll);
random u1 u2~normal([0,0],[v_u1,cov_u12,v_u2]) subject=site;
run;