R on Windows - compile errors - \U used without Hex digits

hoping someone can help me.

I have R 3.2.2 (2015-08-14) and RStudio 0.99.489 on Windows 7. my default working directory is c:\users\adamsben\, but could be anywhere.

I know that when I load a file, such as read.csv("c:\users\adamsben\data.csv") I'll get an error.

Instead I know I need to write: read.csv("c:\\users\\adamsben\\data.csv") or read.csv("c:/users/adamsben/data.csv")

However, I'm getting the same error when I try to compile source code or try to use knitr.

The error I get is:

Error: '\U' used without hex digits in character string starting "'C:\U" Execution halted

Obviously, the error is related to c:\Users\ but now I'm not sure how to fix. I tried changing my working directory, no dice.

Also, I've tried searching for this error on both stackoverflow and google generally, and all I get are people trying to read in data files and needing to change to \\ or /

An example: trying to install shiny devtools::install_github('rstudio/shinyapps')

Downloading GitHub repo rstudio/shinyapps@master
Installing shinyapps
"C:/PROGRA~1/R/R-32~1.2/bin/x64/R" --no-site-file  \
  --no-environ --no-save --no-restore CMD INSTALL  \
"C:/Users/adamsben/AppData/Local/Temp/RtmpIJ5NwN/devtools19c84a7c5e0b
/rstudio-shinyapps-688a4ac"  \
--library="C:/Users/adamsben/Documents/R/win-library/3.2"  \
--install-tests 

Error: '\U' used without hex digits in character string starting "'C:\U"
Execution halted

I really have no idea how to fix something embedded in someone else's code. Any ideas?