请求大佬帮忙看下程序哪里出错了，小白一个论文急需啊啊啊：谢谢谢谢！！
不知道哪里错了，项目区分度难度都不应该是这么大的数字啊。数据的EXCEL放在附件了，是一组25X18个项目的数据谢谢各位大佬！！！
install.packages("ltm")
library(ltm)
setwd("c:/mystudy/RIRT")
ddd<-read.fwf("data1.csv", widths=c(1,rep(1,18)))
dim(ddd)
ddd <- ddd[,-1]
names(ddd) <- paste("It",1:18, sep="")
mod.2pl <- ltm(ddd~z1, IRT.param=T)
mod.2pl$conv
summary(mod.2pl)
coef(mod.2pl)
factor.scores(mod.2pl, method="EAP")

结果：
> setwd("c:/mystudy/RIRT")
> ddd<-read.fwf("data1.csv", widths=c(1,rep(1,18)))
> dim(ddd)
[1] 26 19
> ddd <- ddd[,-1]
> names(ddd) <- paste("It",1:18, sep="")
> mod.2pl <- ltm(ddd~z1, IRT.param=T)
> mod.2pl$conv
[1] 0
> summary(mod.2pl)
Error in solve.default(object$hessian) :
  Lapack例行程序dgesv: 系统正好是奇异的: U[3,3] = 0
> coef(mod.2pl)
            Dffclt       Dscrmn
It1  -1.398595e+09 4.687995e-08
It2  -2.797913e+00 1.694660e-01
It3  -1.398595e+09 4.687995e-08
It4  -5.958137e-01 5.651422e-01
It5  -1.398595e+09 4.687995e-08
It6  -2.154298e+00 1.450527e-01
It7  -1.398595e+09 4.687995e-08
It8  -2.313392e-01 3.893327e+00
It9  -1.398595e+09 4.687995e-08
It10 -2.947178e+00 3.487284e-01
It11 -1.398595e+09 4.687995e-08
It12 -3.548480e-01 3.164737e+00
It13 -1.398595e+09 4.687995e-08
It14 -4.610567e-01 7.744310e-01
It15 -1.398595e+09 4.687995e-08
It16 -1.621804e+01 3.924119e-02
It17 -1.398595e+09 4.687995e-08
It18 -1.802842e+00 2.659201e-01