Same problem here. Have Cubase 5.5.2-64 under Win7-64 with an Intel Core2 Quad and 8GB RAM. Other 32-bit VST's work OK (Arturia, NI, UAD etc) however Jupiter-8 kills the VST bridge.
One other thing I noticed was when running Jupiter-8 standalone, it would always default to the Windows sound driver, instead of the ASIO device driver (MOTU ASIO driver). Even after I had set it and restarted J8, it did not retain the settings. Anyone else seen this? The other synths (CS80 and MgV) retained their audio device settings when closed and restarted.
Maybe Cubase 6 will have a more stable VST bridge?