pdfx option clash inputenc + fontenc + hyperref

I get no error if I load the packages in the correct order:

\documentclass[twoside,a4paper,DIV15,parskip=off,9pt]{scrbook}
% Fonts and typesetting settings
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[ngerman]{babel}
\usepackage[sc]{mathpazo} % For Palatino
%\usepackage{mycals} % What's this????

\usepackage[
  linktocpage=false,      % no page numbers are clickable
  colorlinks=false,       % no color
  breaklinks=true,        % break URLs
  bookmarks,              % creates bookmarks in pdf
  hyperfootnotes=true,    % clickable footnotes
  pdfborder={0 0 0},      % for removing borders around links
  bookmarksnumbered=true, % If Acrobat bookmarks are requested, include section numbers.
  bookmarksopen=false,    % If Acrobat bookmarks are requested, show them with all the subtrees expanded.
  %hidelinks=true,
  %linkcolor=blue,
  %citecolor=blue,
  %urlcolor=blue,
  pdfpagemode={UseOutlines}, % show pdf bookmarks (indices) on startup; does not function all the time
  pdftitle={...}, % title
  pdfauthor={...}, % author
  pdfkeywords={...}, % subject of the document
  pdfsubject={...}, % list of keywords
  pdfmenubar=true,        % make PDF viewer’s menu bar visible
  pdfpagelabels,
]{hyperref}
\usepackage[a-1b]{pdfx}

\urlstyle{same}

% ------

\begin{document}
foobar here
\end{document}

Note that hyperref should be loaded as late as possible, with some exceptions such as pdfx and cleveref.

Also \usepackage{ngerman} should be replaced by \usepackage[ngerman]{babel} and it doesn't make sense to load libertine and doing \renewcommand{\rmdefault}{pbk} if you later do \usepackage{mathpazo}. No need to load url, because it's already loaded by hyperref.

I'm not sure what you think pbk means: it's the symbolic name for Bookman.

I commented mycals, as I know nothing about it.

With pdfx.sty (v1.5.8) the following order of packages works also, provided you change the \usepackage[..options..]{hyperref} into \hypersetup{..options..}.

\documentclass[twoside,a4paper,DIV15,parskip=off,9pt]{scrbook}
\usepackage[a-1b]{pdfx}
% Fonts and typesetting settings
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[ngerman]{babel}
\usepackage[sc]{mathpazo} % For Palatino
...
\hypersetup{%
  linktocpage=false,      % no page numbers are clickable
  colorlinks=false,       % no color
 ...
}

I've put a lot of work, within pdfx.sty, into ensuring compatibility with other packages, and am doing further work to allow it to be loaded at any point within the LaTeX preamble. So I'd appreciate notification of any incompatibility that anyone encounters. Example documents are just what I need.