Error 2503 and 2502 when installing/uninstalling a Windows Installer program

The solution to this issue was a lot more difficult to find online than it should be. This pair of errors usually indicates that access to a temporary file folder has been denied, usually the Temp folder under the Windows folder. For a very simple fix, open an administrative command prompt (right-click the Start button and choose Command Promt (Admin) on Windows 8-10; for Windows Vista/7 hit Start, type cmd, and hit CTRL+SHIFT+ENTER) and paste this:

cacls %WINDIR%\Temp /e /g everyone:f

Try again and it should work!