title: How to access worksheets in EPPlus?
body: <p>I'm using the 3.1 release of EPPlus library to try to access a worksheet in an Excel file.  When I try either of the following methods I get a <code>System.ArgumentException : An item with the same key has already been added</code>.</p>
  
  <pre><code>using (ExcelPackage package = new ExcelPackage(new FileInfo(sourceFilePath)))
  {
     var worksheet = package.Workbook.Worksheets[0];
  
     // OR
  
     foreach (var excelWorksheet in package.Workbook.Worksheets)
     ...
  }
  </code></pre>
  
  <p>Exception Stack:</p>
  
  <pre><code>System.ArgumentException : An item with the same key has already been added.
     at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
     at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
     at System.Collections.Generic.Dictionary`2.Add(TKey key, TValue value)
     at OfficeOpenXml.ExcelNamedRangeCollection.Add(String Name, ExcelRangeBase Range)
     at OfficeOpenXml.ExcelWorkbook.GetDefinedNames()
     at OfficeOpenXml.ExcelPackage.get_Workbook()
  </code></pre>
  
  <p>This seems like very basic functionality to have be so broken.. am I doing something wrong?</p>