This.registry.citationreg.citationById[c[0]] is undefined - ID: 679537859
have received diverse error report with the same problem..
This.registry.citationreg.citationById[c[0]] is undefined
This.registry.citationreg.citationById[c[0]] is undefined
Otherwise, downgrade to the stable version of Zotero from http://zotero.org/download and the error will go away.
After that restart, I just got the error message three days later. Yet, this time, restarting word as well as Zotero and updating the style helped...