SD file.available() not working

Hi, does anyone can use the SD bridge function file.available()? If I try to run the datalogger example ( adding a check for the SD to be written or not:

  // The FileSystem card is mounted at the following "/mnt/FileSystema1"
  File dataFile ="/mnt/sd/datalog.txt", FILE_APPEND);

    Serial.println("file already written");

  // if the file is available, write to it:
  if (dataFile) {

The program always stop on file available. looking at FileIO.cpp does not help so much. Any suggestion? Thanks in advance