TexShop inconsistent behavior

Question

I'm a newbie to Tex, cannot understand how I used MS word soooo long. Here's my first question.

I'm using MacTex which came with TexShop, which so far seems useful. TexShop has a basic LaTex template which until recently worked just fine (i.e. if I hit "typeset" it produced the PDF of a simple document. Here is the template:

\documentclass[11pt, oneside]{article}      % use "amsart" instead of "article" for AMSLaTeX format
\usepackage{geometry}                       % See geometry.pdf to learn the layout options. There are lots.
\geometry{letterpaper}                          % ... or a4paper or a5paper or ... 
%\geometry{landscape}                       % Activate for for rotated page geometry
%\usepackage[parfill]{parskip}          % Activate to begin paragraphs with an empty line rather than an indent
\usepackage{graphicx}               % Use pdf, png, jpg, or eps§ with pdflatex; use eps in DVI mode
                                % TeX will automatically convert eps --> pdf in pdflatex        
\usepackage{amssymb}

\title{Brief Article}
\author{The Author}
%\date{}                            % Activate to display a given date or no date

\begin{document}
\maketitle
%\section{}
%\subsection{}



\end{document} 

Suddendly the template stopped working. But 1-TexShop processes other Tex files just fine, and 2-the offending template above works just fine in Latexian. When I hit "typeset' in TexShop I get the image below. I re-installed MacTex, to no avail. Grateful for any suggestions. Apologies if this is not the right venue for this question.