First of all, this is just a field report!
With R version 3.6.0, some major changes and enhancements have been implemented compared to the previous versions (e.g. R 3.5.3). This means that it became necessary to install the current R version 3.6.1 and to adapt RCall. Julia and R didn’t get along after the R upgrade. After the upgrade I checked the correctness of the register entries and set the path variable to the new R version. But that didn’t help…
I’d like to share my experience with you, which is really important: You have to set the Julia environment variable R_HOME with the R directory:
julia> ENV["R_HOME"] = "C:\\Program Files\\R\\R-3.6.1"
Then build RCall must be executed:
pkg> build RCall
Afterwards the communication between Julia and R went smoothly again.
The solution was already mentioned here, I just wanted to describe it more clearly.