title: Load error for R package 'lmerTest': "package or namespace load failed"
body: <p>I'm unable to get the lmerTest R package to work (it's used to provide statistical tests for objects created with the lme4 package) </p>
  
  <p>When I load it, it gives the following error </p>
  
  <pre><code>Loading required package: Matrix
  Loading required package: lme4
  Error: package or namespace load failed for ‘lmerTest’ 
  in loadNamespace(i, c(lib.loc, .libPaths()), versionCheck = vI[[i]])
  </code></pre>
  
  <p>I've tried removing and re-installing both lmerTest and lme4, in both orders. I'm using the latest R version, both packages are installed in the correct library directory, and there are no permission issues. General solutions to this error when it comes up for other packages have not worked. </p>