Create HTML slides with knitr, Rmarkdown and pandoc

Create HTML slides with knitr, Rmarkdown and pandoc

I am trying to create a HTML slides with knitr, Rmarkdown and pandoc. I
got a reference from
http://rprogramming.net/create-a-slideshow-powerpoint-with-r-knitr-pandoc-and-slidy/.
But I meet a problem at the step5. After executing
##
knit("test4.Rmd")
system("pandoc -s -t slidy test4.md -o test4.html")
##
I got a message
pandoc.exe: Could not parse YAML header:
found character that cannot start any token "source" (line 13, column 1)
Please help me to solve this problem.