# Missing \endscname inserted citation

I am new to LaTeX, and I have encountered an error that I couldn't fix myself.

Error: "Missing \endcsname inserted Три \cite{Бідюк2009}"


Неre is a simple document to recreate an error.

\documentclass[a4paper, 14pt, oneside]{report}

\usepackage{extsizes}
\usepackage[utf8]{inputenc}
\usepackage[T1,T2A]{fontenc}
\usepackage[english, russian, ukrainian]{babel}
\usepackage{indentfirst}
\usepackage{misccorr}

\begin{document}
Один \cite{Congdon2006}

Два \cite{Koch2007}

Три \cite{Бідюк2009}
\bibliographystyle{plain}
\bibliography{sources}

\end{document}


The bibliography document (source.bib):

% Encoding: UTF8

@BOOK{Congdon2006,
title = {Bayesian Statistical Modelling},
publisher = {John Wiley \& Sons},
year = {2006},
author = {Peter Congdon},
pages = {573},
edition = {2},
owner = {Georgii},
timestamp = {2012.04.01}
}

@BOOK{Koch2007,
title = {Introduction to Bayesian Statistics},
publisher = {Berlin: Springer-Verlag},
year = {2007},
author = {Karl-Rudolf Koch},
pages = {249},
owner = {Georgii},
timestamp = {2012.04.02}
}

@ARTICLE{Бідюк2009,
author = {Петро Іванович Бідюк},
title = {Адаптивне прогнозування фінансово-економічних процесів на основі принципів системного аналізу},
journal = {Наукові вісті НТУУ КПІ},
year = {2009},
volume = {5},
pages = {54--61},
owner = {Georgii},
timestamp = {2012.04.01}
}


Both documents are encoded in UTF-8.

-
Depending where your error happens, you should use bibtex8 rather than bibtex to compile your bibliography as bibtex doesn't support UTF-8 encoding. Alternatively, using biber and biblatex could help. –  ArTourter Apr 2 '12 at 19:35
@ArTourter thank you for your help, I'll try to do that. The workaround might be changing identifiers to English without changing the contents of the bibitems. I think, I close the question if i find how. –  GKalnytskyi Apr 2 '12 at 19:56

The error is due to the citation key: it's not allowed to use non ASCII characters in them. So change the Бідюк2009 key into Bidjuk2009 or what you prefer.
Use bibtex and not bibtex8, which doesn't support UTF-8, but only 8 bit code pages such as Latin-1. Instead bibtex won't try to interpret any of the character with high bit set.
You should anyway consider switching to biblatex; the problem with citation keys would remain, though.
@egreg, I think I am using bibtex, and not bibtex8. I don't know because I am using TexStudio and clicked the BibTex button there. Anyway, my mistake was choosing non-ASCII identifiers, so pdfLaTex reported errors. I will look at biblatex later and check if using the combination of XeLaTeX and BibLaTex will help with non-ASCII identifiers. –  GKalnytskyi Apr 2 '12 at 20:24