R module for Windows fails to load

All of the various sets of instructions for building mxnet with R for GPU on Windows have problems so I’m trying to build from source.

I’ve built mxnet branch 1.7.x successfully. I’ve built the R library mxnet.dll successfully.
The error comes when loading the R module, as seen in the source code R/zzz.R,
it fails calling loadModule('mxnet') giving ERROR: loading failed.

I can’t work out what loadModule is trying to do, and why it is failing. Any ideas?

.onLoad <- function(libname, pkgname) {
  library.dynam("libmxnet", pkgname, libname, local=FALSE) # SUCCESSFUL
  library.dynam("mxnet", pkgname, libname)                           # SUCCESSFUL
  loadModule("mxnet", TRUE) # ERROR: loading failed