Bibtex with url (with %-sign) in note-field wont compile

Question

I have the following reference and the URL is causing the document to fail to compile. Tried everything I could think of. How to get this to work?

@misc{prodromou2010ostatus,
title={{OStatus 1.0}},
author={E. Prodromou and B. Vibber and J. Walker and Z. Copley},
note={\url{http://ostatus.github.io/spec/OStatus%201.0%20Draft%202.html} Accessed: 23.6.2017},
year={2010}
}

Answer 1

With biblatex you should not use the note field to give the URL and date of access of a webpage. Instead use the dedicated fields url and urldate. url can deal with all kinds of characters that are special for TeX, as it is interpreted in verbatim mode.

@online{prodromou2010ostatus,
  title   = {OStatus 1.0},
  author  = {Evan Prodromou and Brion Vibber and James Walker and Zach Copley},
  date    = {2010-08-30},
  url     = {http://ostatus.github.io/spec/OStatus%201.0%20Draft%202.html},
  urldate = {2017-06-23},
}

The problem in your example indeed arose due to the %. In the .bbl many fields (amongst them note) are saved in the format

\field{<fieldname>}{<fieldcontent>}

If <fieldcontent> contains a % character, that % is interpreted as start of a comment and everything after it is ignored. That means in particular that the curly braces don't close, grouping is messed up and everything goes pear shaped. So in general one should avoid % and other special characters in fields, unless the fields are verbatim fields such as url. This also holds for fields that you do not see in the output, but are still recognised by biblatex - one of these is abstract which is often pre-filled if you download a .bib file from the internet and may contain all sorts of characters that cause trouble if the exporting tool was not careful. Even if your style does not print the field, problematic characters there can still mess things up.

Note that even though Biber is recommended over BibTeX nowadays, in this instance switching to Biber does not help. You should still consider using Biber, though. _{In case of problems with the abstract field BibTeX is a bit more forgiving than Biber in some situations. But that should not be an argument to prefer BibTeX.}