This error is occurring because your R packages are installed on a network drive (\userfs/myuser/w2k) rather than on your local computer. This causes problems for R when it looks for files during RStan model compilation. You’ll need to move your package directory to a local folder on your computer.
If you’re not sure how to do that, I’ve previously written up some instructions in this post. That post assumed that the new package directory should be in C:\Users\R, so just update that if you want it somewhere else