Be Careful Naming Your Images...

Short version: an image with a name starting "ID-" and ending in a number throws up errors.

Long version:
I had a product that should have sold - I was offering it at 1/4 the price on Amazon, but despite being featured it never did. So today I looked at the product. I thought it looked good, maybe I had uploaded a lousy picture - so I clicked on the second pic and a small screen pops up: Error 501 CODE NOT IMPLEMENTED /.php or something like that.

I went into a panic, I'd just done a move to a new host and my first thought is that it must have been some script injected into the image. I go offline, run a scan, nothing found. I download the image and compare it byte for byte with the original image I'd saved to disc months ago - it's identical.

I tried taking a new photo and uploading it - same error.
I deleted the product and recreated it - same error
I delteted the product and recreated it with a 3rd new photo - same error.

All my other images and additional images were working.
Then, on a whim I changed the name of the image.
It had been ID-Stamper_1.JPG
I named it Stamper_1.jpg

And the errors went away. Interesingly enough, the main image was called ID-Stamper.JPG and it worked fine like that, (I had to change it to Stamper.JPG to get the additional photo to show) so I guess it's the combination of ID and a number, or something in the handler for additional images but from now on I'll be avoiding that naming combination.

PS: I'm running 1.3.9h powered by a Linux Server, from the comfort of a cheap leather swivel chair in my home office powered by Doritos.

You should be reporting that problem to your hosting company's server administrator so they can fix the problem

I agree. Other than potential issues with Google Merchant Center feeds, Zen Cart doesn't really care what the name of the image file is. And even that isn't really a Zen Cart problem.