I wrote a risk assessment of the Heroku platform in Latex this term. It was my first large report using Latex, I ran into the following error and it look me a long time to figure out.

``````Runaway argument?
Author(Year{\natexlab {{}})]{natbib_key} Author. \newblock Author u\ETC.
! Paragraph ended before \@lbibitem was complete.
\par
l.257
``````

What this means is that the you cited more than 26 time for the same Author in the same year (Heroku, 2015). The problem was this: `\bibliographystyle{plainnat}`. This style, quite reasonably, sets the letter limit. Too bad the error message is just so awful.

The key step was opening up `.bbl` file and see to see `\natexlab {{}})natexlab` where the `{{}}` were missing a letter - vs the earlier citations.

## TL;DR

``````-  \bibliographystyle{plainnat}
+  \bibliographystyle{abbrv}
``````

`abbrv` is likely the correct format anyway for scientific publications and is likely already in your class file (but I didn’t have one of these).