There is a bug in older versions (before 1.12) of PassiveTeX causing euro characters (€, which should look something like “€”) to appear as black boxes.

This bug is fixed in the Red Hat Linux passivetex-1.11-5 package, available in rawhide.

However, you'll need an up to date marvosym.sty file, which you can get from CTAN. (The current Red Hat Linux rawhide teTeX package has this updated already, but marvosym.sty is much smaller to download!)