You can NOT load Wherigo on an Oregon 600. Wherigo is/was only available on Colorado and the old Oregon (3/4xx) as they had a Wherigo player.
I also have an Oregon 600 but for Wherigo I use WhereYouGo on my Android tablet.
I discovered the same thing for my new Garmin Oregon 650. I wish they'd make that clearer on their web site. It say's specifically that if you have a Garmin Oregon it will work. Wrong. If you have an earlier model it will work. No biggie, I'll use in on my Motorola Moto G.