# “! You can't use \end' in internal vertical mode.” Error

I am using TEX editor and have written the following code:

\documentclass[10  pt,a4paper,twoside,reqno]{amsart}
\usepackage{amsfonts,amssymb,amscd,amsmath,enumerate,verbatim,calc}
\renewcommand{\baselinestretch}{1.2}
\textwidth = 12.5 cm
\textheight = 20 cm
\topmargin = 0.5 cm
\oddsidemargin = 1 cm
\evensidemargin = 1 cm
\pagestyle{plain}
\begin{document}
\title{Some Title}
\author{My Name}
\date{July 25, 2015}
\maketitle
\abstract{Some text....
......................}
\section{Introduction}
Some text.....
.............

\end{document}


When I click "Quick Build" I get the following error ! You can't use \end' in internal vertical mode. on Line 27 (Line containing \end{document}). Please explain why does this error occur and how should I got about fixing it.

The abstract for an amsart document should be given in environment for
\begin{abstract}

Given as just \abstract, TeX is collecting a box, and you can't end the run the document in that situation. As there's no \end{abstract} you never close the box properly.