I seem to be having this same problem, however the suggested fixes are not working. I have EZ Keys 64 bit working as stand alone, but do not find it as an available plug-in instrument to studio one. I have EZ Drummer 3 and EZ Bass which appear to be working as intended. If I go to Product Manager, I see the EZ Keys bundles , Grand Piano and Studio Expansion. They both are asking to install updates, but the updates are the 32 bit versions.
