! Illegal parameter number in definition of \NewValue

Question

Everything works fine until I added the following URL reference to my references.bib file. The URL reference is output but I am getting the error

Illegal parameter number in definition of \NewValue.

in addition.

@misc{jdk,
  author = {Oracle},
  title = {Platform, Standard Edition 7
Development Kit},
  howpublished = {\url{http://www.oracle.com/technetwork/java/javase/jdk-7-readme-429198.html#contents}},
  note = {Accessed: 2015}
}

MWE:

\documentclass{article}
\usepackage[backend=bibtex]{biblatex}
%\bibliography{references} 
%\addbibresource{<database>.<extension>}
\addbibresource{references.bib}
\begin{document}
Hallo world\cite{einstein} I do not if it \cite{jdk} Tree Tree bla bla will work test \nocite{Doe:2009:Online}
\printbibliography
\end{document}

Answer 1

You should use the url and urldate, rather than howpublished and note:

\begin{filecontents*}{\jobname.bib}
@misc{jdk,
  author = {Oracle},
  title = {Platform, Standard Edition 7 Development Kit},
  url = {http://www.oracle.com/technetwork/java/javase/jdk-7-readme-429198.html#contents},
  urldate = {2015},
}
\end{filecontents*}

\documentclass{article}

\usepackage[backend=bibtex]{biblatex}

\DefineBibliographyStrings{english}{%
  urlseen={Accessed:}% %%% not `visited on'
}

\addbibresource{\jobname.bib}

\begin{document}

Hello world\cite{einstein} I do not if it \cite{jdk} will work test
\nocite{Doe:2009:Online}

\printbibliography

\end{document}

Note that the filecontents* environment is just to make the example self contained and you can use your file (after modifying it as suggested).

Answer 2

In case anyone comes here for the same reason I did, this was because I had the special character # in the title of a paper I was citing. (In particular, http://people.csail.mit.edu/shaih/pubs/01perm.pdf .) The error message was pretty inscrutable, gave me the the wrong line numbers, only showed up on the second compilation when I introduced it, and was accompanied by other messages like

illegal parameter number in definition of \abs@field@title
illegal parameter number in definition of \abs@field@journal

I figure I'll throw those lines in here for Googleability. In my case, I had to change

title="Zero-one permanent is #P-complete, a simpler proof"

to

title="Zero-one permanent is \#P-complete, a simpler proof"

and re-compile.