title: Error "Index vectors are of different classes: numeric date"
body: <p>I am trying to implement the following code from the following site:</p>
  
  <pre><code>library(quantmod)
  library(tseries)
  library(timeDate)
  
  symbols &lt;- read.csv("sp500.csv", header = F, stringsAsFactors = F)
  nrStocks &lt;- length(symbols[,1])
  
  z &lt;- zoo()
  for (i in 1:nrStocks) {
    cat("Downloading ", i, " out of ", nrStocks , "\n")
    x &lt;- get.hist.quote(instrument = symbols[i,], start = dateStart,
      quote = "AdjClose", retclass = "zoo", quiet = T)
    z &lt;- merge(z, x)
  }
  </code></pre>
  
  <p>but I get the error message:</p>
  
  <pre><code>Error in download.file(url, destfile, method = method, quiet = quiet) : 
    cannot open URL 'http://chart.yahoo.com/table.csv?s=MFE&amp;a=0&amp;b=01&amp;c=2008&amp;d=8&amp;e=12&amp;f=2011&amp;g=d&amp;q=q&amp;y=0&amp;z=MFE&amp;x=.csv'
  In addition: There were 50 or more warnings (use warnings() to see the first 50)
  
  In merge.zoo(z, x) : Index vectors are of different classes: numeric Date
  </code></pre>
  
  <p>Any ideas?</p>