> 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?

I just ran this and had no problems at all - is everything up-to-date?
Maybe you could post the actual error message.

Cheers,  Phil Ratcliffe