Blank Page and "Missing \begin{document}" error in simple document

Blank Page and "Missing \begin{document}" error in simple document

Im new with LaTeX, I have MikTek and TeXnic Center. The first time I tried
to write a document I noticed I couldn't cancel terms in mathematical
equations, so iI download the cancel package and installed it by hand.
Now the new package is working (or at least that is what I think), but for
example the following simple document generates a Missing \begin{document}
error and a first blank page:
\documentclass{article}
\usepackage[spanish,activeacute]{babel}
\usepackage{amsmath}
\usepackage{cancel}
\title{...}
\author{...}
\begin{document}
\maketitle
\begin{equation}
\cancel{a}
\end{equation}
\end{document}
I cant copy all the build output from the TexnicCenter output window, but
here you can see some part of it
Why is this?