Thanks lan. I thought I had properly installed the .pak files, but obviously hadn't as you suggested. As a result of your reply I repeated that procedure. I'm not sure what I did wrong the first time, ...
Funny, I received an email a few hours ago telling me there was a reply to this.
When I click on the link provided I get a message saying "The topic or post you requested does not exist".
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After a couple of years not using JamStix, I've just installed JamStix 3.6.1 32 bit. I'm using Reaper 4.75 32 bit, and Win 8 64 bit. Install seemed OK.