[Greolt]

The first thing I would suspect is that the background.jpg is not in the exact same directory path.

If you are sure that is correct then the next thing would be the Mach version you are using.

I have had a version, as I update to the latest usually, that did a similar thing and when I went back to a previous version all was OK.

So if you're not on the latest lock down version already, then try that.

And if you are already, try stepping back a version or two.

Greg