Broken category images

[Icarus]

Hey everybody,

I am having a weird problem.
I am using an import process to import categories and products.
Some categories have images, others have a blank field in the image column.

The categories with no image are showing a broken image on the front office.
I did not notice this until now, since FF does not show them, but in other browsers, I see a broken image.

This is happening only on categories that have sub categories in them.
So the front office page shows a broken image for the category, and broken images for its sub categories.

Anyone familiar with this problem and its solution?

TIA.