def SGErrors(IErr):
    """
    Interprets the error message code from SpcGroup. Used in SpaceGroup.
    
    :param IErr: see SGError in :func:`SpcGroup`
    :returns:
        ErrString - a string with the error message or "Unknown error"
    """
    ErrString = [' ', 'Less than 2 operator fields were found',
        'Illegal Lattice type, not P, A, B, C, I, F or R',
        'Rhombohedral lattice requires a 3-axis',
        'Minus sign does not preceed 1, 2, 3, 4 or 6',
        'Either a 5-axis anywhere or a 3-axis in field not allowed', ' ',
        'I for COMPUTED GO TO out of range.',
        'An a-glide mirror normal to A not allowed',
        'A b-glide mirror normal to B not allowed',
        'A c-glide mirror normal to C not allowed',
        'D-glide in a primitive lattice not allowed',
        'A 4-axis not allowed in the 2nd operator field',
        'A 6-axis not allowed in the 2nd operator field',
        'More than 24 matrices needed to define group', ' ',
        'Improper construction of a rotation operator',
        'Mirror following a / not allowed',
        'A translation conflict between operators',
        'The 2bar operator is not allowed',
        '3 fields are legal only in R & m3 cubic groups',
        'Syntax error. Expected I -4 3 d at this point', ' ',
        'A or B centered tetragonal not allowed', ' ',
        'unknown error in sgroup', ' ', ' ', ' ',
        'Illegal character in the space group symbol']
    try:
        return ErrString[IErr]
    except:
        return 'Unknown error'
