title: error message when opening Excel file created using xlsx package R
body: <p>I have created an Excel file using the xlsx package in R.  When I go to open the file I get an error message:
  Excel found unreadable content in this workbook.<br>
  Do you want to recover the contents of this workbook?</p>
  
  <p>I select yes and it doesn't appear like anything is missing.  Does anyone know why this is happening?  I found another stackoverflow question about this same issue but for a different program </p>
  
  <p><a href="https://stackoverflow.com/questions/27711270/error-message-after-creating-xlsx-file-using-java">Error Message after creating XLSX file using java</a></p>
  
  <p>My R and OS information is below.   </p>
  
  <p>R version 3.2.1 (2015-06-18)
  Platform: i386-w64-mingw32/i386 (32-bit)
  Running under: Windows 7 x64 (build 7601) Service Pack 1 </p>
  
  <p>The code I have been using for the Excel file is:</p>
  
  <pre><code>#create excel workbook for output data
  surveyresults_2015v4&lt;-createWorkbook( )
  
  #export catch data to output file
  c_data&lt;- createSheet(wb=surveyresults_2015v4, sheetName="catch_data")
  addDataFrame(x=datag, sheet=c_data,row.names=FALSE,showNA=F )
  saveWorkbook(surveyresults_2015v4, "surveyresults_2015v4.xlsx")
  </code></pre>