def _ensureError(self, err, dataVals=None):
        """Check error validity"""
        if err is None:
            err = self.fw.errorVals

        vals = self.checkError(err, dataVals)

        if vals is None:
            pg.warn('No data error given, set Fallback set to 1%')
            vals = np.ones(len(dataVals)) * 0.01

        try:
            if min(vals) <= 0:
                pg.critical("All error values need to be larger then 0. Either"
                            " give and err argument or fill dataContainer "
                            " with a valid 'err' ", min(vals), max(vals))
        except ValueError:
            pg.critical("Can't estimate data error")

        return vals