在用lme拟合线性混合效应模型时出现下列问题怎么破？在线等，急con<-lmeControl(maxIter = 15000, msMaxIter = 15000, tolerance = 1e-3)

lme.fit<-lme(YY~t_ij1+I(t_ij1^2),random=~t_ij1+I(t_ij1^2)|x_index,data=datal,control = con)
Error in lme.formula(YY ~ t_ij1 + I(t_ij1^2), random = ~t_ij1 + I(t_ij1^2) |  :
  nlminb problem, convergence error code = 1
  message = function evaluation limit reached without convergence (9)