Arnold can't render Birfrost fluid

[mj1e20]

I used maya 2018 version and got an error that is / /Error: [mtoa.translator] bifrostTranslator: Arnold node type bifrost_polymesh does not exist.

[Stephen.Blair]

Do you have Bifrost installed?

The bifrost_polymesh node is part of Bifrost. That node, and others, are defined in arnold_bifrost:

C:\Program Files\Autodesk\Bifrost\Maya2018\2.2.1.0\bifrost\arnold-6.2.0.0\arnold_bifrost.dll