mclapply warning

 When I run the 35 line, I got the Warning message:
In mclapply(content(x), FUN, ...) :
  all scheduled cores encountered errors in user code

When I run the 37 line, I got the message: "Error in UseMethod(\"words\") : \n  no applicable method for 'words' applied to an object of class \"character\"\n", simpleError in UseMethod("words"): no applicable method for 'words' applied to an object of class "character"