吴喜之教授的《复杂数据统计方法》第52页代码运行后总是报错，请教大家如何解决？谢谢！

w=read.csv("diabetes.csv") #先将excel文件转换为csv
require(nnet);require(caret);set.seed(1010)
mygrid=expand.grid(.decay=c(0.5,0.1),.size=c(4,5,6))
nnetfit=train(y/max(w[,1])~., data=w, method="nnet",maxit=1000, tuneGrid=mygrid, trace=F)

Error in `[.data.frame`(data, , all.vars(Terms), drop = FALSE) :
  undefined columns selected


print(nnetfit)