Yes, today for the second time - none of the solutions seem to match my problem (either that, or I'm reading them wrong). There are no residual Paint.NET versions on my computer, I've looked with the Windows Installer Cleanup Utility and REVO Uninstaller. Neither is this an uninstallation problem, since, well, the program didn't install to begin with. I didn't get any error messages about the assembly, or any error messages with numbers that came up before the setup wizard with the Paint.NET logo started up. I didn't move Paint.NET after it installed (because, well, it doesn't install), and I can't get to the Paint.NET repair utility because, again, the program doesn't install.
I tried installing it again, and it's the same problem - after it creates the system restore point, the installer says "the system cannot find the file specified." I have no idea what file it's looking for. And yes, I did "Run as administrator".