There is a bug in 2.0.4 of the Help module where it checks where you can move the items to. For a quick fix run this in the SQL window.
ALTER PROCEDURE {databaseOwner}[{objectQualifier}Help_ListCategoryActiveByParent]
@ModuleID int,
@ParentID int
AS
SELECT [CategoryID],
[CategoryGUID],
[Name],
[Description],
[Image],
[KeyWords],
[ModuleID],
[Order],
[Level],
[Parent],
[Visible],
[Deleted]
FROM {databaseOwner}{objectQualifier}Help_Category
WHERE [Parent] = @ModuleID AND [ModuleID] = @ParentID
AND [Deleted] <> 1
AND [Visible] <> 0
ORDER BY [Level] ASC,
[Parent] ASC,
[Order] ASC
GO