[MiKTeX] AMS font problem

[Bernice B. <jb...@co...>]

My document starts with the following preamble:

\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}


The only unusual symbol I'm using is $\nmid$. Latex runs fine and the 
log file seems to be clear (Winedt log scan finds nothing). However, YAP 
gives an error message and does not display the character. What must I 
do to make this work?

-- Jeff Barnett