R caret package train

R caret package train

I am getting an error in below R code. Code needs "caret" package. any help?
traininginput <- as.data.frame(runif(1000, min=0, max=100))
trainingoutput <- sqrt(traininginput)
#Column bind the data into one variable
trainingdata <- cbind(traininginput,trainingoutput)
colnames(trainingdata) <- c("Input","Output")
indx <- createFolds(trainingoutput, returnTrain = TRUE)afdshas
ctrl <- trainControl(method = "cv", number = 2, index = indx)
nnetGrid <- expand.grid(.decay = c(0.01, .1), .size = c( 11, 13),
.bag = FALSE)
set.seed(100)
nnetTune <- train(x = traininginput, y = trainingoutput, method =
"avNNet", tuneGrid = nnetGrid, trControl = ctrl, preProc =
c("center", "scale"), linout = TRUE, trace = FALSE, MaxNWts = 200,
allowParallel = FALSE, maxit = 1000)
Error in `[.data.frame`(data, , "pred") : undefined columns selected