Error in opening new Markdown file

File > New File > R Markdown
Fill in dialog box, click OK. Markdown file opens with no heading. Get the following error at console:

Error in .Call(C_serialize_to_yaml, x, line.sep, indent, omap, column.major, :
Incorrect number of arguments (9), expecting 8 for 'serialize_to_yaml'

RStudio version 1.1.456
R version 3.5.1
All packages updated except for XML -- error when trying to update.

I've quit session and restarted; I've opened different projects, but the problem still persists.
Thanks for any insight.

This might be worth a shot: delete and reinstall the yaml package. Answerer on SO indicated that did the trick:


Thank you -- that was the fix!