def METHOD_NAME(self, files):
    """
    Return the number of files failed
    """
    self.acquired.commit()
    self.available.commit()
    self.failed.commit()
    self.completed.commit()
    for i in files:
        # Check each set, instead of elif, just in case something has
        # got out of synch
        if i in self.available.files:
            self.available.files.remove(i)
        if i in self.completed.files:
            self.completed.files.remove(i)
        if i in self.acquired.files:
            self.acquired.files.remove(i)
        self.failed.addFile(i)