Error in function(i) : task 2 failed - "non-character argument" on R

Question

What is Error in funcion_2(i) : task 2 failed - "non-character argument"??.

I'm trying to create a list of list , extracting words from xml files named on "lista".

cl <- makeCluster(mc)
registerDoParallel(cl)
list_of_list <- foreach(i=lista_xmls, .packages='XML') %dopar% funcion_2(i)
stopCluster(cl)

lista_xmls is ...

lista_xmls <- c("1.xml", "10.xml", "100.xml", "1000.xml", "10000.xml")

class(lista_xmls[1])

[1] "character"

funcion_2 is ...

funcion_2 <- function (archivo) {
#archivo = paste(archivo, ".xml", sep = "")

dataa <- xmlParse(archivo)

xml_data <- xmlToList(dataa)

titulo <-  is.vacio(xml_data$metadata$obaa$general$title)

t <- strsplit(titulo, " ")
t <- unlist(t, recursive = TRUE, use.names = TRUE)

descripcion <-   is.vacio(xml_data$metadata$obaa$general$description)

d <- strsplit(descripcion, " ")
 d <- unlist(d, recursive = TRUE, use.names = TRUE)
 # d <- d[nchar(d) > 2]

doc = xmlTreeParse(archivo, useInternalNodes = TRUE)
 # node <- getNodeSet(doc ,"general")
  palabras <- xpathApply(doc, "//keyword", function(n) xmlValue(n[[1]])) 
  #df <- data.frame(matrix( c( titulo,descripcion,rep( 1, each=length(palabras) ) ) , nrow=1, byrow=T))
  #colnames(df) <- c("title","description",unlist(palabras))

  atsil <- c(t,d,palabras)

  #atsil <- unlist(atsil)
  atsil <- list(atsil)
  return(atsil)

}

Rstudio respond Error in funcion_2(i) : task 2 failed - "non-character argument", but I don't even know what does that mean, what is causing it, nor how to overcome it?

testing funcion_2 it does return a list with the words, soo I belive the error is in %dopar% ,it doesn't work with %do% , nor ...

results2 <- foreach(i=lista, .packages='XML') %dopar% funcion_2(as.character(i))

This is my first question in Stack and I'm begginer on R programing