Sorry this is causing pain. What's the text of the error message?
In R, true and false are written in all caps, TRUE or FALSE. That is, your bit of code should read na.rm = TRUE. That may be causing your issue.
If not, could you create a very minimal reprex of your R Markdown doc to demonstrate us what's going on? FAQ: What's a reproducible example (`reprex`) and how do I do one?