I tried a few hours later and it worked without the warning. The warning I was getting was one of these
Sorry Beebster I disagree. The advert fr Paint.net is large. Its not a ful screen, but along with the 3 others it is. It's on their promotional page, and they are suggesting it. I had not heard of paint.net until they advertised it. They are endorsing using it, plain and simple.
It's good though, I'm glad I persisted. I had tried GIMP, and as Craig says te interface is hostile. There is one tool that my Sketcbook pro software (The equivalent I guess of Adobe illustrator, from Autodesk), the replace colour. This works much better than my fill tool.
Craig, I'd say it's worth a go, it's a free tool and works well. You don't get Paint.net from paint.net, they sell industrial paint. But you can get it from here.
http://www.dotpdn.com/downloads/pdn.html