These assemblies are from the old version of the SharePoint editor (for SharePoint 2003). Perhaps the errors are caused by migrating from a SPS 2003 site to MOSS 2007? Check your web.config files and see if there are leftover settings for RadEditor, RadWebParts, and RadSpell. The problematic Web.config file could be in the SharePoint web site root folder, in the wpresources folder under the web site root, or in the \Program Files\Common Files\Microsoft Shared\web server extensions\wpresources\ folder.
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