Dirk is right in this case, BUT if the .libPaths() does not work, then please also check if you have the latest packages.
I am posting this as an ancillary answer backup which I ran into with the shiny package backend switch of their code needing Rcpp! 
In this case of getting the "no package" error message, I fixed it by:
- Selecting - devtoolspackage and then using this line below. (if you don't have devtools then get it with- install.packages("devtools")
 
- devtools::install_github("rstudio/shiny")
 
The development version of the package handled this better, and added the package as a dependency.
Mods - I realize this is an answer to an old question, but I might help others not wasting an hour like I just did.