Keep in mind that some maps' downloads have been forever lost because of the times we've been hacked.
You can also tell there is a discrepancy in the number of map threads and maps available for download in that the top left says we have about 3400 maps in the database even though our Map IDs are numbered almost to 5000. I don't know how many of these are because of maps being deleted though.
So yeah, it is natural that some DLs might not work (could also be because of other reasons). modified by JungleTerrain