public class AllDecimalRule : ValidationRule
    {
        private readonly decimal _min, _max;        

        public AllDecimalRule(decimal min, decimal max)
        {
            _min = min;
            _max = max;
        }

        public override ValidationResult Validate(object value, CultureInfo cultureInfo)
        {            
            decimal _value = 0;

            try
            {
                if (((string)value).Length > 0)
                {
                    _value = decimal.Parse((String)value);
                }
                else
                {
                    return new ValidationResult(false, null);
                }
            }
            catch (Exception)
            {
                return new ValidationResult(false, null);
            }

            if ((_value < _min) || (_value > _max))
            {
                return new ValidationResult(false, null);
            }
            else
            {
                return new ValidationResult(true, null);
            }
        }

TextBox myTextFakt_91 = new TextBox();            
myTextFakt_91.TextAlignment = TextAlignment.Right;                
myTextFakt_91.DataContext = _myDataRow;
bind = new Binding("[1]")
   {
      Converter = new myConverter(),
      ConverterParameter = _strFormat1,
   };
bind.ValidationRules.Add(new AllDecimalRule(_minFakt,_maxFakt));
myTextFakt_91.SetBinding(TextBox.TextProperty, bind);
myGridVip.Children.Add(myTextFakt_91);