You don't say what file type the image is. Some file types do not allow
paint because they are scalable vector graphics and have no pixels to paint.

Ah, thanks, that makes sense SVG from Inkscape. How can I convert it to jpg so I
can edit it? I'm trying to erase the outlines of the shapes to send to a DIY 3D
Printer guy in hopes he'll make me a part.

Maybe I should just send the SVG instead. But the visible shaddows aroung the
pieces used to make the composite image might confuse him or the program to make
the layers.

SVGs are not very widely used. You can open the SVG into the GIMP then save
it as a JPEG. Then you should be able to edit the file and paint on it.
Vector graphics are scalable so make sure it is the right size before you
save as JPEG.

i wouldnt edit an image in jpg
as jpg uses lossy compression
so every generation gets more blurred.

Edit as a tif, or gimp format,
then maybe save the last version as a small GIF
if its a line drawing?

I agree with not using jpg. First thing I do is save to png. Non-lossy
format has the advantage of being widely used on the internet in web
pages. I have been told that files are larger than when saved in jpg
and that I blame on compression that makes lousy picture quality. Try
png and see what you think. png also works for combining different
forgrounds and backgrounds because it offers transparency.

I sometimes wonder if gimp would be more popular if people would bother
looking over and following some of the tutorials on the gimp website.

Yes, but if you are using an svg to start with you don't have much detail to
lose, but your point is well taken. Png is superior, but it is not as widely
used as jpg. I agree that xcf is a good format, but the file sizes are huge
in comparison to either png or jpg with png being larger than jpg. It is a
trade off files size for detail, but you need the detail to begin with to
make the larger file size worthwhile. Svg does not support the colour range
and detail to warrant it, IMO. Also you cannot send an xfc to just anyone.
They need to be a GIMP user or it is useless.