Fix for xdvipdfmx:fatal: pdf_ref_obj(): passed invalid object.
Caveat Lector: This blog post was published 8 years ago. Depending on the content, it may no longer be applicable or relevant.
This happened to me when embedding an EPS file into a xelatex document.
The fix (for me) was to add the binaries directory /usr/local/texlive/2016/bin/x86_64-linux to the PATH environment variable.
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