Thanks Jason. Sorry its been a while, but just looking at this now.
I changed the input button code to:
<input type="button" class="deleteButton" value="" onclick="document.getElementById('WADADeleteRecordID').value=<?php echo($row_WADAactivities['ActivityID']); ?>;document.getElementById('WADADeleteRecordName').innerHTML='<?php echo($row_WADAactivities['Activity']); ?>';document.getElementById('deleteBox').style.display = 'block';document.getElementById('deleteMessage').style.display = 'table';" />
And changed the message to include:
This will permanently remove the following keyword: <span id="WADADeleteRecordName">name</name>.<br/>
Its partly working - the Activity is being displayed correctly, but nothing after that, including the delete and cancel buttons.