This error occurs because the area called "Main" is damaged. In this case, its column value for vw_area.area_childlist, which will normally contain at least a copy of the vw_area.pageid field, is empty. How was the Main area created? Have you made any changes to the area recently, or received errors when creating/editing the area?
Under normal operation, the area_childlist column should always have a value, except for a race condition when the pageid column is not populated yet; however, in that case, you would not be able to access the area yet and would not be able to trigger this error.