ImageMagick went poof?

Something changed this weekend. I hope somebody can offer me some help. I use Imagemagick; convert (and mogrify) to create thumbnails on one of my sites. It worked like a breeze but since friday I get the error:

ERROR: exec() error: sh: /usr/X11R6/bin/convert: No such file or directory

Where did it go, anybody knows? :)

Thanks,
Rense

Using whereis, I found them at: /usr/bin/convert and /usr/bin/mogrify.

Regards,

Bob S.