J-8V v1.1 is also not working for me (Intel iMac, 2.4GHz Core 2 Duo, 4GB, OS X 10.5.4, everything updated).
I've done the dongle out-download syncrosoft-install-dongle in dance more times than I care to remember. Prophet V works just fine. Syncrosoft is now at v5.4.8.6. The rest of my Arturia V collection is just fine.
My symptom is that when J-8V runs, it just comes up with a blank white window (the right size, but empty), and the menu items in the menu bar aren't populated except with generic entries.
When you click over the blank window, you can see the app is partially working as there are (white) shapes drawn, but the app itself never loads. The same happens on v1 that came on CD, the v1.1 download, and even the v1.1 demo download.
Anyone else seeing this? Antoine is on the case, but it seems to be taking a long time. I'm interested to hear if anyone else is seeing these symptoms -- maybe even a workaround. It smells like something is incompatible somewhere.