I Spent a frustrating hour assisting an end user from NB (Danny Goddard) who's Windows 10 machine had suffered from a known issue where .jar files were opening with internet explorer instead of java.
the result was that when you double click the REDapp icon, it would try and open in internet explorer, with horrible error handling and ultimately confusing and frustrating the end user.
The user did nothing wrong, and in fact had done everything right, but suffered this end result.
The known solutions were:
1) reinstall java (This did not work)
2) manually edit the .jar entry in the registry (Which I felt was too extreme for an end user)
Fortunately, a wonderful HeroUberNerd (Johann N. Löfflmann) on the internet, had suffered this one too many times and wrote his own fix for the issue:
Here is a link to the fix he wrote and instructions on how to use it. It fixed the issue immediately.