New Post: Library in a different folder in vb

An R engine that has properly initialized should pick this up (i.e. this path should be present in .libPath(), and:

library(drc) 

from R or R.NET Rengine.Evaluate should work.
I am not sure this is what you ask for. Is the R line you give working from R but not from R.NET?

As a last resort setting an environment variable R_LIBS can specify a particular path to look in. I actually use this personally.

> Sys.getenv('R_LIBS')
[1] "f:/Rlib"