         </td>
 
         {for column in MANIFEST_COLUMNS[1...]
-          <td>{metadata?[column] ? <span className="form-help">?</span>}</td>}
+          <td key={column}>{metadata?[column] ? <span className="form-help">?</span>}</td>}
 
         <td>
           <button onClick={@removeSubjects.bind this, filenames...}>&times;</button>

          </p>

          <ul>
            {for line in @state.log
              if line instanceof Error
                <li style={color: 'red'}>{line.toString()}</li>
              else
                <li>{line}</li>}
          </ul>
        </div>
      </Route>

      <tr key={filenames.join()}>
        <td>
          {for filename, i in filenames
            <div key={filename}>
              {filename}
              {unless files[i]?
                <span className="form-help error" title="Missing image">&nbsp;<i className="fa fa-exclamation-circle"></i></span>}
