R help - Oct 2014 - n-gram error with packages tau, tm, RTextTools

Hi:

I am trying to compute n-grams using package tm and tau with following code:

tokenize_ngrams <- function(x, n=3)
return(rownames(as.data.frame(unclass(textcnt(x,method="string",n=n)))))
texts <- c("This is the first document.", "This is the second
file.",
"This is the third text.")
corpus <- Corpus(VectorSource(texts))
matrix <- DocumentTermMatrix(corpus,control=list(tokenize=tokenize_ngrams))


And getting following error

 Error in FUN(X[[2L]], ...) : non-character argument


also getting same error using the RTextTools package.

Any solution?

Best regards:

John