title: Cannot load package in R
body: <p>Since yesterday, I cannot load some common used packages, e.g. <code>reshape2</code> and <code>stringr</code> through library command. </p>
  
  <p>Step to reproduce my problem:</p>
  
  <p>1) Start a new session in Rstudio server (Version 0.99.467). I also kill the active-sessions in Rstudio server. </p>
  
  <p>2) Run these codes</p>
  
  <pre><code>library(ggplot2)
  library(stringr)
  </code></pre>
  
  <p>3) Get an error message:</p>
  
  <blockquote>
    <p>Error in unloadNamespace(package) : 
      namespace ‘stringr’ is imported by ‘reshape2’ so cannot be unloaded
     Show Traceback</p>
  </blockquote>
  
  <p>Rerun with Debug</p>
  
  <blockquote>
    <p>Error in library(stringr) : “stringr” version 0.6.2 cannot be unloaded.</p>
  </blockquote>
  
  <p>But I don't get error if <code>stringr</code> is loaded before <code>ggplot2</code>. How should I fix this problem. Thanks for any suggestions. </p>
  
  <p>I may have to update R to 3.2</p>
  
  <p>My R session info:</p>
  
  <pre><code>R version 3.1.3 (2015-03-09)
  Platform: x86_64-pc-linux-gnu (64-bit)
  Running under: Ubuntu precise (12.04.5 LTS)
  
  locale:
   [1] LC_CTYPE=en_AU.UTF-8       LC_NUMERIC=C               LC_TIME=en_AU.UTF-8        LC_COLLATE=en_AU.UTF-8    
   [5] LC_MONETARY=en_AU.UTF-8    LC_MESSAGES=en_AU.UTF-8    LC_PAPER=en_AU.UTF-8       LC_NAME=C                 
   [9] LC_ADDRESS=C               LC_TELEPHONE=C             LC_MEASUREMENT=en_AU.UTF-8 LC_IDENTIFICATION=C       
  
  attached base packages:
  [1] stats     graphics  grDevices utils     datasets  methods   base     
  
  other attached packages:
  [1] ggplot2_1.0.0
  
  loaded via a namespace (and not attached):
   [1] colorspace_1.2-4 digest_0.6.4     grid_3.1.3       gtable_0.1.2     MASS_7.3-39      munsell_0.4.2    plyr_1.8.1      
   [8] proto_0.3-10     Rcpp_0.11.2      reshape2_1.4     scales_0.2.4     stringr_0.6.2    tools_3.1.3    
  </code></pre>