在做离散选择实验模型，用mlogit拟合过程中，总是提示如下错误：
> res1<-mlogit(RES~1 | oval+pyd+weeping+nocol+lcb+lcl+ldt+nobd|gender,data=dataset11,shape="long",alt.var="ALT")
Error in solve.default(H, g[!fixed]) :
  Lapack routine dgesv: system is exactly singular: U[11,11] = 0
> summary(res1)

Call:
mlogit(formula = RES ~ 1 | oval + pyd + weeping + nocol + lcb +
    lcl + ldt + nobd, data = dataset11, shape = "long", alt.var = "RES.ids",
    method = "nr", print.level = 0)


有人知道怎么解决吗？？