The problem is that tekkit is using an older version of nether ores, the newest version is here
How to fix
1. Open the mods folder delete mod_NeatherOres.jar
2. Click here to download the latest version (direct link via dropbox)
3. Extract the GenerateNetherOres_Bukkit.jar to the mods folder
4. Run the launch.bat it will come up with an error
5. Open the config folder & open GenerateNetherOres.cfg in notepad
6. Change the Block ID to 135 & enableMaceratorRecipes to true
7. Save & close, & that's it
