When trying to knit a simple test document using the ACM format, I get the following error:
! LaTeX Error: Environment Shaded undefined.
See the LaTeX manual or LaTeX Companion for explanation.
Type H <return> for immediate help.
...
l.45 \begin{Shaded}
pandoc: Error producing PDF
Error: pandoc document conversion failed with error 43
Execution halted
I can knit the same document as regular PDF with no problem.