Problems when extracting attributes from an XML file using R

I'm having problems trying to extract data from an XML file (the data is stored as attributes and not as elements, if I'm right). I'm using R 3.1.2 on Windows 7 with RStudio.

The file (shortened) looks like this:

<?xml version="1.0" encoding="ISO-8859-1" ?> 
<MensajePredicionesEolicas>
 <CodElemento Zona="Espana">
  <PotInstalada valor="22751000" /> 
   <FechaFichero valor="2014120907" /> 
   <Detalle>
    <FechaDato valor="2014-12-09">
     <HoraDato valor="7">
      <Prediccion valor="10588564" /> 
      <Percentil10 valor="9563875" /> 
      <Percentil90 valor="11435276" /> 
     </HoraDato>
     <HoraDato valor="8">
      <Prediccion valor="10269849" /> 
      <Percentil10 valor="8588400" /> 
      <Percentil90 valor="11623841" /> 
     </HoraDato>
     <HoraDato valor="9">
      <Prediccion valor="9823678" /> 
      <Percentil10 valor="7840628" /> 
      <Percentil90 valor="11536093" /> 
     </HoraDato>
    </FechaDato>
   </Detalle>
 </CodElemento>
</MensajePredicionesEolicas>        

For example, to extract the values of the atrribute FechaDato I've tried:

data <- xmlParse("file.xml")
date.pred.path <- "//CodElemento[@Zona='Espana']/Detalle/FechaDato"
date.pred <- sapply(data[date.pred.path], xmlGetAttr, "FechaDato")  

I'm obtaining empty lists. Any ideas? Thanks in advantage.