RStudio aborted when running code in Rmd file

Question

I have this weird problem: when I am running a code chunk (or every code chunk) in an Rmd file in RStudio, it says Error in readRDS(mapfile) : unknown input format basically for every line, and then R session was aborted saying , even when I Cmd+S the file.

But everything works very well if I copy the code and run them in the console. How can I solve this? I assume this should be an Rmd problem? Thank you all!