\documentclass[a4j, 11pt, report]{jsbook}
\pagestyle{empty}
\usepackage{ascmac}
\usepackage[dvipdfmx]{graphicx}
\graphicspath{{../images/}}
\西暦
\usepackage{url}
\usepackage{plext}
\usepackage{natbib}
\bibpunct[:]{(}{)}{;}{a}{}{;}
\usepackage[at]{easylist}
\usepackage{subcaption}
\usepackage[T1]{fontenc}
\usepackage{txfonts}
\usepackage{tabularx}
\newcounter{excerpt}
\setcounter{excerpt}{0}
\newcounter{lnum}
\newcommand{\lnum}[0]{\refstepcounter{lnum}\texttt{\thelnum}}
\newcolumntype{R}{>{\raggedright\arraybackslash}X}
\newenvironment{excerpt}[2]{%
\setcounter{lnum}{0}
\begin{table}[htbp]
\small
\refstepcounter{excerpt}
\textgt{データ\theexcerpt }#1\\
\label{data:#2}
\begin{tabularx}{\linewidth}{llX}}{%
\end{tabularx}
\end{table}
}
\begin{document}
\begin{excerpt}{テスト}{test}
\lnum & B: & ほげほげ\\
\lnum & C: & ふがふが\\
\lnum & B: & ぴよぴよ\\
\end{excerpt}
\end{document}
以下エラー：
Call `platex test_bg.tex'
This is e-pTeX, Version 3.14159265-p3.7-160201-2.6 (utf8.euc) (TeX Live 2016) (preloaded format=platex)
restricted \write18 enabled.
entering extended mode
(./test_bg.tex
pLaTeX2e <2016/09/08> (based on LaTeX2e <2016/03/31> patch level 3)
Babel <3.9r> and hyphenation patterns for 83 language(s) loaded.
(/usr/local/texlive/2016/texmf-dist/tex/platex/jsclasses/jsbook.cls
Document Class: jsbook 2016/09/08 okumura, texjporg
(/usr/local/texlive/2016/texmf-dist/tex/platex/jsclasses/jslogo.sty))
(/usr/local/texlive/2016/texmf-dist/tex/platex/base/ascmac.sty
(/usr/local/texlive/2016/texmf-dist/tex/platex/base/tascmac.sty))
(/usr/local/texlive/2016/texmf-dist/tex/latex/graphics/graphicx.sty
(/usr/local/texlive/2016/texmf-dist/tex/latex/graphics/keyval.sty)
(/usr/local/texlive/2016/texmf-dist/tex/latex/graphics/graphics.sty
(/usr/local/texlive/2016/texmf-dist/tex/latex/graphics/trig.sty)
(/usr/local/texlive/2016/texmf-dist/tex/latex/graphics-cfg/graphics.cfg)
(/usr/local/texlive/2016/texmf-dist/tex/latex/graphics-def/dvipdfmx.def)))
(/usr/local/texlive/2016/texmf-dist/tex/latex/url/url.sty)
(/usr/local/texlive/2016/texmf-dist/tex/platex/base/plext.sty)
(/usr/local/texlive/2016/texmf-dist/tex/latex/natbib/natbib.sty)
(/usr/local/texlive/2016/texmf-dist/tex/latex/easylist/easylist.sty)
(/usr/local/texlive/2016/texmf-dist/tex/latex/caption/subcaption.sty
(/usr/local/texlive/2016/texmf-dist/tex/latex/caption/caption.sty
(/usr/local/texlive/2016/texmf-dist/tex/latex/caption/caption3.sty)
Package caption Warning: Unsupported document class (or package) detected,
(caption) usage of the caption package is not recommended.
See the caption package documentation for explanation.
)) (/usr/local/texlive/2016/texmf-dist/tex/latex/base/fontenc.sty
(/usr/local/texlive/2016/texmf-dist/tex/latex/base/t1enc.def))
(/usr/local/texlive/2016/texmf-dist/tex/latex/txfonts/txfonts.sty)
(/usr/local/texlive/2016/texmf-dist/tex/latex/tools/tabularx.sty
(/usr/local/texlive/2016/texmf-dist/tex/latex/tools/array.sty)) (./test_bg.aux)
(/usr/local/texlive/2016/texmf-dist/tex/latex/txfonts/omltxmi.fd)
(/usr/local/texlive/2016/texmf-dist/tex/latex/txfonts/omstxsy.fd)
(/usr/local/texlive/2016/texmf-dist/tex/latex/txfonts/omxtxex.fd)
(/usr/local/texlive/2016/texmf-dist/tex/latex/txfonts/utxexa.fd)
(I search kanjifont definition file: . . ) (I search font definition file: . .
. . . . . ) (/usr/local/texlive/2016/texmf-dist/tex/latex/txfonts/t1txr.fd))
Runaway argument?
! File ended while scanning use of \TX@get@body.
<inserted text>
\par
<*> test_bg.tex
?
! File ended while scanning use of \TX@get@body.
というエラーですので，なにか単純な制御文字の抜けがあるのだと思うのですが，発見できません．
どうぞお力をお借りできますと幸いです．