I have exactly the same problem with the Reference3.dll of Sonarworks (32-bit version!), Headphone Calibration plug-in. I successfully added de VST dll on a Notebook with Windows 7 64 bit and JRiver Media Center v 21.0.23.
However, I am unable to add the same 32-bit VST dll in JRiver Media Center c 21.0.23 on a Windows 10 64-bit version, latest edition i.e. Microsoft's November 2015 iteration. I contacted Sonarworks Support, but sofar they have not been able to help me resolve this issue.
I deleted the VST file, installed it again, but every time I want to add the VST file, and I point to the folder where the Reverence3.dll ist stored, JRiver Media Center returns the error message "Failed to install the plug-in".
I also tried it on the Windows 10 64-bit notebook, prior to the latest MS update iteration. To no avail as well. I had hoped the new Windows 10 iteration would resolve it, but it didn't.
Anyone who can advise me? Just for your information: I bought a license for 3 x VST plugins from Sonarworks (Headphone Calibration plugin). So, it should install on the second Notebook with Windows 10 as well.