The jscript_imagehover.js file is present in both the folders you mention,

includes/templates/classic/jscript
includes/templates/template_default/jscript

Should there only be one occurrence of it?

Incidentally, not worked this out yet as new to Zen, what template is being used on my site?
classic or template_default, I have assumed it is classic as files uploaded there for mods work fine.