knitr to pdflatex converter for lyx

Question

I am writing a book using LYX, have been using it for several years. Some time ago, maybe close to a year, evidently after updating R, MikTeX, LYX, I started getting a dialog saying that my installation does not include a knitr to pdf converter, but I can use an external converter if I authorize it, which I do and things work. But I have to do this every time I compile a new pdf file from LYX. Does someone know why I am missing the converter, and how I can add it (have updated MikTeX many times, which doesn't do it)?

A secondary question: It seems that the knitr to pdflatex converter controls the magnification of the pad file upon opening (over-riding Acrobat Pro DC 2017 magnification settings), and produces too small a magnification, that I have to increase every time I compile LYX to pdflatex. Any suggestions on how to fix this very annoying problem.

Thanks a ton for any help anyone can provide.

Doug Martin

The dialog message I get upon trying to compile the LYX file to pdflatex:

\., LyX: An external converter requires your authorization 

The requested operation requires the use of a converter from
knitr to pdflatex: 

Rscript --verbose --no-save --no­restore $$s/scripts/lyxknitr.R $$p$$i $$p$$o $$e $$r

This external program can execute arbitrary commands on your system,
including dangerous ones, if instructed to do so by a maliciously
crafted LyX document
\ti/ould you like to run this converter? 
Only run if you trust the origin/sender of the LyX document!  

Do not run      Run     Always run for this document

Have searched Stack Exchange and other resources for an answer, but have not received one. Doug

Answer 1

According to this message:

https://www.mail-archive.com/lyx-devel@lists.lyx.org/msg197583.html

the questions were added to protect against malicious code. Another message later in that thread says one of the preference settings would let you disable the checks.