The error: "Undefined Control Sequence. Overfull hbox (15.0pt too wide)" appears for each "end tabularx." I have tried {noindent} before \say{begintabularx} without success. While I could continue working for the first 500+ instances of this error, now the document will not render.

Error Messages <https://ibb.co/5Y4DtCS>

Rendered <https://ibb.co/nBWSSth>

```
\documentclass{book}
\usepackage{changepage}
\usepackage{comment}
\usepackage{dirtytalk}
\usepackage[T1]{fontenc}
\usepackage[hang,flushmargin]{footmisc}
\usepackage{geometry}
\usepackage{graphicx}
\usepackage{imakeidx}
\usepackage[utf8]{inputenc}
\usepackage{lettrine}
\usepackage{lipsum}
\usepackage{microtype}
\usepackage{marginnote}
\usepackage{pifont}
\usepackage{tabularx}
\usepackage{type1cm}
\usepackage{yfonts}
\geometry{paperwidth=8.5in,paperheight=11in,inner=1in}

\usepackage{perpage}
\MakePerPage{footnote}

\usepackage{afterpage}

\newcommand\blankpage{
    \null
    \thispagestyle{empty}
    \addtocounter{page}{-1}
    \newpage
    }

\begin{document}

\begin{center}
\say{Undefined Control Sequence.\\
Overfull hbox (15.0pt too wide) in paragraph at lines 53 and 63 and 75.\\
- these are the \say{end tabularx} lines.}
\end{center}

\begin{tabularx}{1\textwidth} { 
    >{\full\arraybackslash}X 
    >{\full\arraybackslash}X  }

\begin{center}
\noindent \textbf{Header Left Column}
\end{center}
 &
 \begin{center}
\noindent \textbf{Header Right Column}
\end{center}

\end{tabularx}

\begin{tabularx}{1\textwidth} { 
    >{\full\arraybackslash}X 
    >{\full\arraybackslash}X  }

\noindent \lipsum[3]
 &
\noindent \lipsum[4]

\end{tabularx}

\bigskip

\begin{tabularx}{1\textwidth} { 
    >{\full\arraybackslash}X 
    >{\full\arraybackslash}X  }

\noindent \lipsum[5]
 &
\noindent \lipsum[6]

\end{tabularx}

\bigskip

\noindent Why the error for \say{end tabularx?} I am using overleaf.com in Firefox 81.0 on OSX 10.15.6. I have tried {noindent} before \say{begintabularx} without success. The usecase is a polyglot book, with one language in the left column and a different language in the right column. The two columns must begin on the same line, but are not required to end on the same line.

\bigskip

\noindent Many thanks for your help.

\end{document}

```