It's a dependency for libX11.so.6 in the libs/ directory.
mv libX11.so.6 no-libX11.so.6
cured the problem for me.
edit:
that of course means "use your system libX11 and not the one provided inside the libs/ directory". I wonder if one should try to use as many libs as possible from the system and revert to the ones provided with the client only if something goes wrong. I had also to disable libasound (and use the system one).