fullname package is very old: its release date is March 1992, which means it was written for LaTeX 2.09.
\cite making it lose its robustness. It's possible to robustify it, but a trick is needed, because
\MakeRobust is fooled by the fact that normally
\cite is robust.
However, when the trick is used, LaTeX fails with “TeX capacity exceeded”.
You can work around the issue by using
\cite is in a moving argument. My advice is to use a more recent and robust citation package such as
Here's a minimal example:
(The .bib file is one I used for another answer.)
You could also do
\protect is not necessary any more. But, again, this is like trying to repair your great-grand-father's bike you found in the basement. Nice hobby, but just that.