Yes, this error is thrown during Export.
I've tried to isolate it by deselecting all, then just adding some specific objects. Exports work with just webparts, or just page templates, or just stylesheets, but if I select just Pages, then it throws the error.
Refreshing View_CMS_Tree_Joined doesn't seem to help, but we do have a couple of custom Views used in the page types. However, we didn't manually write those views, they were generated by the portal app.
Here's the query for the view:
CMS_Category.CategoryDisplayName AS CategoryDisplayName, CMS_Category_Parents.CategoryDisplayName AS ParentCategoryDisplayName
LEFT OUTER JOIN
CMS_Category AS CMS_Category_Parents ON CMS_Category.CategoryParentID = CMS_Category_Parents.CategoryID