This is so very irritating. I was completely happy with the previous version and only updated because prompted, just to get this ridiculous fatal error. I have too much stress to deal with to apply the suggested solution, since I do not understand it and would have to put effort into checking what it is, since obviously I now don't trust just doing what (get)paint.net says.
I wanted to change the colours of a certain image to the Ukrainian ones for obvious reasons, and it's very sad that I now can't.