My hopes aren't high on getting this solved, but I figured I'd give it a shot. Googling the issue has been pretty inconclusive, possibly since I don't have any specific error descriptions.

As has been mentioned elsewhere, I recently got a new computer, and have been transferring some files from one to the other. One, however, (the one I really want/need to use of course) is confounding me. Basically, I've been world-building for a long time and have been working on a map. As I'm neither an artist nor cartographer, it's just a simple jpeg I've been drawing in MSPaint. I'm aware the program is mostly junk, but it was simple to use for my simple needs, and things were fine.

The new computer, however, is choking on that file. A simple blue line suddenly has a centimeter of blue "fuzz" surrounding it. Dustings of color are faded and blocky, as if awkwardly cut and pasted from a background that didn't match. Put simply, the drawing looks hideous and is ruined. I tried emailing it to myself instead of copying to disk, with no change. I saved it into every format Paint is capable of and transferred them all, with mostly the same results. One of them is slightly less awful. I downloaded GIMP, opened and saved it on the old computer, brought it over, and opened it in GIMP here. Exactly the same problem. I assume this is something to do with the custom colors I used, to help differentiate separate regions with similar but non-identical climates. Beyond that, though, I have no idea how to fix the problem, and I'd really prefer to not have to choose between "settle for least ruined version" or "redraw 8000x4000 pixel map". The old computer won't live forever, so using it every time I want to work isn't a permanent solution, aside from being really inconvenient in itself.