Error "RegCreateKeyEx failed, code 5"

Symptom: on Windows, no maps appear, downloads fail, and a console start prints:

Error: Could not open/create prefs root node Software\JavaSoft\Prefs at root 0x80000002. Windows RegCreateKeyEx(...) returned error code 5.

What it means

RouteConverter stores its settings through Java's preferences, which live in the Windows registry. Error code 5 is Windows "access denied": Java may not create its Software\JavaSoft\Prefs key. Root 0x80000002 is HKEY_LOCAL_MACHINE. A locked-down work PC without registry rights is the typical case. It was reported with Java 8 update 201; the JDK fix for it is part of Java 9 and later and of Java 8 update 202 and later.

What to try

1. Use a current download. The Windows download bundles its own Java runtime (see RouteConverter for Windows), so a recent release does not depend on an old Java 8 on the machine. If you start the .jar with your own Java, update it to Java 8 update 202 or later, or better a current version.
2. Create the key yourself. With administrator rights, create the registry key HKEY_LOCAL_MACHINE\Software\JavaSoft\Prefs that the message names. Without those rights, ask your IT department.
3. Run it from a portable launcher. In the forum thread, running RouteConverter through the jPortable Launcher from PortableApps.com worked for one tester and not for the reporter, so treat it as an experiment.
4. Use another computer. If the PC stays locked down, convert on a private machine.

The Windows download page covers launch and SmartScreen; RouteConverter.exe cannot save files covers a different Windows permission problem.