Quote:The box was unticked. I tried " ticking " it and repeated the process which resulted in the same error.
Leave it unticked. Not the way to remove an alpha channel. It just does what it says, automatically adds one when an image is imported.
Remove an alpha channel using Layer -> Transparency -> Remove Alpha Channel (also a right click on a layer context menu)
The jpeg works because a jpgs' do not support transparency.
You can also tell from the layer name bold type = no alpha channel regular type = has an alpha channel.
There is that as an animation: https://i.imgur.com/RJ9m4af.mp4