What's the reason that readRDS doesn't seem to work in Windows?

I'm trying to make the my code portable to Windows and realized that even though I use file.path to create paths still the readRDS function won't work, for example:

file.exists('C:/temp/HarvardX-Skillability/data/rds/Users.rds')
> TRUE
readRDS('C:/temp/HarvardX-Skillability/data/rds/Users.rds')
> Error in readRDS("C:/temp/HarvardX-Skillability/data/rds/Users.rds") : 
  error reading from connection

I also tried:

 file.exists('data/rds/Users.rds')
 > TRUE
 readRDS('data/rds/Users.rds')
 > Error in readRDS("data/rds/Users.rds") : error reading from connection

Why is that? and how can I fix it? In Ubuntu 18.04 works perfectly ...