At first Jamstix 4 Manager didn't see internet connection. I've tryed everithinbg, like temporary turn off antivirus - it just kept show me error message.
Next day it got fixed itself somehow, but Jamstix 4 VSTi keeps crushing on Reaper's VST plugins scan.
It worked with Cakewalk, but... Well, with that kind of start, I'm afraid it's better not to continue.