problem loading packages

I have successfully installed, loaded and used R packages many times in the past, but for whatever reason when I try to do it now I get error messages. As an example, both stringr and magrittr appear to be installed, but when I try to load stringr I get the following:

library(stringr)
Error: package or namespace load failed for ‘stringr’:
.onLoad failed in loadNamespace() for 'magrittr', details:
call: fun(libname, pkgname)
error: object 'magrittr_init' not found

Suggestions appreciated.

At a quick guess you need to install the magrittr package.

however are you sure stringr is installed?