In PPM, there is no Windows binary for the current version (1.8.9) of plyr, even though there is one on CRAN and there are binaries on PPM for (at least) MacOS and Ubuntu.
As far as I can tell, none of the limitations described at Serving Package Binaries - Posit Package Manager apply here.
Thanks for the report, we'll take a look. It is possibly related to an incident yesterday with missing binary packages.
This turned out to be a separate but related issue with recent Windows binaries specifically. We should have plyr binaries back up now, and are working to restore other missing Windows binaries.