Judging from the traceback, it’s not clear to me whether you directly attempted to create an RDS file or not. I’m not even sure if those error messages come from your own R code or not.
It would help if you gave the exact set of steps that you used.
@makarov: Please don’t double-post to our channels (this forum, GitHub, StackOverflow, specifically). It diffuses our answers and can lead to us answering the questiont twice and we’re pressed for time as it is.