I’m having exactly the same problem but with Waldorf Edition 1.7.3 on my Windows 7 64-bit, Cubase Studio 64-bit 5.5.3. I got the plug-in’s latest installer, a 64-bit version, from Waldorf Support, but no matter what I tried, the plug-ins (3 DLL files Attack, D-Pole, and PPG Wave) always get black listed. The 64-bit installer installs both a 64-bit version and a 32-bit version, but neither seem to register correctly with Cubase Studio 5.5.3. I notified Waldorf’s support and am waiting for a response. My hypothesis is that Waldorf’s new DLLs for this plug-in do not validate against VST standards.