your screen shot indicates that this was created with the old version of iRite, and that iRite is not isntalled in Dreamweaver.
to edit the iRite instance, you will need to have iRite installed.
Personally, I would remove the iRite code form this page, upgrade to Data Bridge, and use the new version of Data Bridge to add the new version of HTML Editor to the page. When configuring HTML, in the preset editor, you will options to enable spell checking.