title: Error message running the example from the reshape2 help page
body: <p>My code, which was running without problems before, crashed when calling the dcast formula. After playing around, I found out that even the minimal example from the help page of dcast does not work for me anymore. More precisely:</p>
  
  <pre><code>#Air quality example
  names(airquality) &lt;- tolower(names(airquality))
  aqm &lt;- melt(airquality, id=c("month", "day"), na.rm=TRUE)
  
  acast(aqm, day ~ month ~ variable)
  acast(aqm, month ~ variable, mean)
  </code></pre>
  
  <p>The last line produces the following error: </p>
  
  <pre><code>Error in vaggregate(.value = value, .group = overall, .fun = fun.aggregate,  : 
    could not find function ".fun"
  </code></pre>
  
  <p>Here is my sessionInfo():</p>
  
  <pre><code>R version 2.13.1 (2011-07-08)
  Platform: x86_64-pc-mingw32/x64 (64-bit)
  
  locale:
  [1] C
  
  attached base packages:
  [1] grid      stats     graphics  grDevices utils     datasets  methods   base     
  
  other attached packages:
  [1] ggplot2_0.8.9   proto_0.3-9.2   reshape2_1.1    xtable_1.5-6    reshape_0.8.4   plyr_1.5.2      lubridate_0.2.5
  
  loaded via a namespace (and not attached):
  [1] stringr_0.5  tools_2.13.1
  </code></pre>
  
  <p>I don't come up with a satisfying answer of what is going wrong here, so I would appreciate some help. Also, I found the following thread here on stackoverflow: <a href="https://stackoverflow.com/questions/4835202/error-with-custom-aggregate-function-for-a-cast-call-in-r-reshape2">Similar problem</a>
  This problem seems to result from a custom function. I, however, use the standard mean function and a standard example from the help page. </p>
  
  <p>UPDATE: I just did some internet research and did not find any information regarding an update of the reshape2 package. This was the best guess I had regarding the problem.</p>
  
  <p>UPDATE2: The problem occurred because I most probably reassigned the mean function while I was playing around with a statisctic example during an R session. Restarting R solved the problem. Now, everything works as expected again.</p>