Hang on, it could be that
OPCODE6DIR64 has not been added to the system variables? Can you check? Just open the command line and run
You should see an entry for
OPCDE6DIR64, if not the installer didn't add it, in which case, I need to update the installer. In the mean time, simple set
OPCDE6DIR64 to point to the plugins64 dir from within the Csound root folder.