And it's your own damn faults for engaging in thread necromancy. This mod has been out of date since beta 1.5_01 as it says in the thread title. Go here where the mod has been picked up by another modder: http://www.minecraftforum.net/topic/639823-123x-ray-n-dtdb/
http://www.minecraftforum.net/topic/639823-123x-ray-n-dtdb/
It would work if you are on a 1.5.01 beta server and using a 1.5.01 beta client.
The thread for the updated mod is here:
http://www.minecraftforum.net/topic/639823-125x-ray-n-dtdb/