def wrong_value(value_name, decorator_name):
    """
    Retrieves the "wrong value at decorator" error message.

    :param value_name: Wrong value's name
    :param decorator_name: Decorator name which requires the message.
    :return: String - Wrong value at decorator message.
    """
    return "ERROR: Wrong " + value_name + \
           " value at " + decorator_name + \
           " decorator."