On validating our site pages when I had the administration visible we received an error to say one of the image tags was not closed. This occurs on a course admin block not on the home page admin block.
<tr class="r0"><td class="c0" valign="top" width="16">
height="16" width="16" alt="">
Does anyone know where I can change this to add the missing /> to the end of this line or why it isn't isn't included?