Error with function kfold in package dismo

Dear list members,

I got this error in package "dismo".

fold <- kfold(bradypus, k=5)
 > bradytrain <- bradypus[fold != 1, ]
 > me <- maxent(predictores, bradytrain)
Error en .readRowsAscii(raster, rows[i], 1) : elemento 1 esta vacio;
   la parte de la lista de argumentos  '>' ha sido evaluada:
    (startcol, 1)

Function maxent works perfect for "bradypus" (data frame with 116 
observations), but it doesn't work for "bradytrain" when I use kfold 
function.
"bradytrain" is also a data frame but with 93 observations.  The message 
is in Sapnish, but basically say that element 1 is empty.
  Thank you very much in advance.
  Best,

Manuel

Manuel Sp?nola, Ph.D.
Instituto Internacional en Conservaci?n y Manejo de Vida Silvestre
Universidad Nacional
Apartado 1350-3000
Heredia
COSTA RICA
mspinola at una.ac.cr
mspinola10 at gmail.com
Tel?fono: (506) 2277-3598
Fax: (506) 2237-7036