TeX embedding fails

Issue Summary

I have installed DruTeX on my drupal 4.7.2 installation. Everything seemed fine. I get this message from the DruTeX toolbox:

The temporary directory is writable.
The image directory is writable.
Executing "latex" was successful: This is pdfeTeX, Version 3.141592-1.30.5-2.2 (Web2C 7.5.5)
Executing "dvipng" failed. Either dvipng isn't installed or the "dvipng" executable is not in one of the search paths.
You cannot use dvipng for rendering images (check the conversion method above).
Executing "convert" (ImageMagick) was successful: Version: ImageMagick 6.3.5 10/01/07 Q16 http://www.imagemagick.org

So I switched to ImageMagick Conversion.
But when I try to insert an expression, like $x^2$, it always says "TeX embedding failed!".
The first error message I encounter in the log is this:

Command: convert -density 107 -trim tmp/drutex-***.dvi files/tex/***.png
Return value: 1

Could anybody explain me how to fix it? I do need this module working properly.
Thank you.