Unable to display large versions of images

I cant get large images to show. When the popup opens, it's empty. An example:

http://heksebua.com/zcshop/courage-p-1000.html?zenid=c64afc98ba4e71622a81b1e25bf4019b

Medium pictures show up, but not large.

All medium pictures are in the images/medium folder, and have the suffix _MED and a lower case extension

All large pictures are in the images/large folder, and have the suffix _LRG and a lower case extension

All images are jpg
All the names are the same.
The settings are, from what I've been able to find, correct.

It's been like this since I first installed Zen Cart.
I searched the forums and the FAQ without finding this exact problem, so I thought I'd better post it.

I'm using Zen Cart 1.3.9h
I've updated it but not upgraded.

I'm using the arch shoppe template

The add-ons I've got are related to payment options and shipping, or simple side boxes. Nothing related to images.

It's running on Apache with MySQL. I've had it running on three different servers, with the same problem. So it's not server related.

I hope you can help me with this issue as soon as possible.

Linda

Consider installing Image Handler 3. This module takes care of image issues. After installing it you need only ONE image, in the main images folder - that being your large image. No need for MED or LRG anymore.

Thanks. I'll look into that.