report/courseoverview/index.php has a page rendering bug. When you click view with no available data for that combination of course and time period the XHTML page structure is not build correctly:

line 277 column 1 - Warning: discarding unexpected </td>
line 277 column 6 - Warning: discarding unexpected </tr>
line 277 column 11 - Warning: discarding unexpected </table>
line 258 column 37 - Warning: <table> attribute "width" has invalid value "*"