Try running Jamstix.exe manually first, located in C:\jamstix3\bin\64 as an administrator and then see if Jamstix will run properly.
So I went to that folder and there was no Jamstix.exe file. There was this file in the bin\32 folder, so I copied it into the bin\64 folder and did what you said and now it works.
I don't know why and don't know how you figured it out, but you have given me a workaround, thanks! Hope there is a fix for me so I don't have to do that every time though!
The "cannot open core event" is always caused by the plugin server not running I have found. Ralph would have to explain the technical aspects of what actually is going on there but I can speak from experience.
When you installed Jamstix did you choose to install the 64bit vst? If you chose to only install the 32bit vst, that is probably why it was in the \bin\32 folder and not \bin\64.
It's been so long ago, I cannot remember, but thought I had. It seems to be working after I copied the exe file into the bin\64 folder. I sent Ralph the updated log file with it working for him to check out.