Hi Jocelyne,
We’ve never seen symptoms like this before, so a bit of sleuthing will be required to work out what’s going on here.
It would be worth checking for any errors reported in the Shaderlight Message Window (accessible from the Window menu in Shaderlight).
Could you try saving to a variety of different locations besides the desktop, just in case there’s something peculiar about the desktop on your system. Could you also try a variety of different image formats, in case the problem is related to specific formats.
Are you viewing the ‘Current render’ tab in Shaderlight, and have you waited until the render has fully completed before saving? Although Shaderlight is supposed to save the current state of your render whether it has finished or not, we should check that we’re on the same page as you in our testing here.
Many thanks, and apologies for the problems you’re experiencing with Shaderlight,
Shaderlight support