The definition for the Blog_Categories in 5.04.02 (haven't checked later or earlier releases) has a problem in the nonclustered index definition for IX_Blog_Categories_PortalID .  Specifically, it has ALLOW_PAGE_LOCKS set to OFF.

The side effect is that maintenance plans which perform reindexing operations will fail with an error message similiar to the following:

Executing the query "ALTER INDEX [IX_dnn_Blog_Categories_PortalID] ON [..." failed with the following error: "The index "IX_dnn_Blog_Categories_PortalID" (partition 1) on table "dnn_Blog_Categories" cannot be reorganized because page level locking is disabled.". Possible failure reasons: Problems with the query, "ResultSet" property not set correctly, parameters not set correctly, or connection not established correctly.

The fix is to alter the index using the following statement to turn page locks back on (which is the default for sql server):

ALTER INDEX [IX_dnn_Blog_Categories_PortalID] ON [dbo].[dnn_Blog_Categories] SET (ALLOW_PAGE_LOCKS = ON)

I'm not sure why you guys have page locks turned off for that table, but this is not good practice.

This table will be removed in the future, it will only exist in the 5.0 Blog release to allow for category migration (to the core).