That is because most users are not aware of the fact the Minecraft and most Mods shift their ItemIDs by 256.
So if you set your ID to 6000 in the config, it will actually be 6256 ingame.
And welcome to the world of the Mod Pack makers. This is something we need to look after with EVERY single mod, as some some don't shift the IDs and some do.
Indeed, and let me expand on Lathanael's post. It is also very valuable to learn to use the tool "grep". Launching NEI and asking for item id enumerations and then doing math to switch them down to unshifted IDs is slow.
If I'm looking for id conflicts I open a terminal in my minecraft installation directory and proceed thusly:
Code:
grep -i conflict ForgeModLoader*0.log
This usually shows me conflict warnings in the log. Let's say that I know ID 30190 (this one comes up for a lot for me) is a problem. I'd use extended grep like this:
Code:
grep -RiE '=30190$' config/*
This shows me every file where a line ending in "=30190" exists. I can then change one. Usually I try and change the newer file, but sometimes it's not clear who to change (e.g., one time gregtech had a bug and forestry had new content and I had to sort it out). But usually the next step is to see "Oh wow, there are like 20 item ids that conflict." So what I need is 20 item IDs. I keep a notebook of unassigned ranges I know about, but I
always double check this after starting up minecraft a few times because my notes could be wrong. With 110 mods in my pack, it pays to be careful.
So I might say, "I know that around 2150 is open and I need 20 ids". I can ask grep for this:
This looks for any assignments that look like "=2150" through "=2169". Pretty handy. Grep is great.