I'm having the same problem and i found that its got to be something to with the server side and not the client side tho since using the Tekkit client and starting a single player world the macerator works fine with the Nether Iron and Nether Gold there like it should, it produces 4 dust for each nether ore put in.
In looking at the "NetherOresCore.class" file there are 2 lines that are for gold and iron and not for the rest of them, not sure if that makes a difference or not tho, i'm not really good with java:
My guess from the code is that they are trying to pull in the items for gold dust and iron dust and that's not loading properly, perhaps they are called something else or there is a different way to refer to them.
Also in that list of macerator stuff it doesn't include Nether Copper or Nether Tin both of which macerate into 2 regular ores per, which goes into 2 dusts if run thru again, thereby giving 4 dust per nether ore for Nether Copper and Nether Tin .
So...wherever the Ic2Recipes.addMaceratorRecipe is listed f the Nether Copper and Nether Tin, would be the best place to look to find out how best to fix the Nether Gold and Nether Iron.