It is looking for the VST plugin, which is a .dll file, not the standalone app which is the .exe file.

The one for Nectar is called iZNectar3.dll.

In my computer it is found in C:\Program Files\Steinberg\VSTPlugins

I don't use Real Band here, but I assume it must have a function where you can scan for new plugins, maybe someone else can help you with that aspect.