Quote from Galadh
My wife and me, we're having terrible problems with aligning the Thermal Expansion items' IDs to Ars Magica mod's IDs.
Basically, first mishap came when AM's pure essence overwrote all copper ingots in recipes. When we finally handled it by switching
AM pure essence's ID to different digit (hell, having 45 mods gets into a habit of tweaking IDs ) different AM's essences started to disappear from Creative Mode inventory + recipes...
I honestly do not know whether it should be posted here - in TE's thread, but it was TE's installation which started problems in the first place, so...
I just hope some of you guys can figure it out, cause we are at a loss trying to re-fit the IDs over and over again... You get one item back - two other go missing - you get those back - three more disappear... ID mismatches pop up everywhere...
As a server operator with about 70 mods, and having gone through several major updates, your best bet is making a spreadsheet or at the very least text file with the block and ID ranges of the IDs you have assigned to the mods. Blocks can go up to 4096, and I think Items up to 32000. Plenty of room in there if you start out with a plan. Finding free numbers in a world that has already been generated is a little rougher when you are not trying to corrupt an existing world. I would suggest using NEI's ID function to give you a list of free IDs.
Asking mod authors to fix your ID conflicts is considered bad form, because the problem doesn't lie with the mod, but your ability to configure it properly. If you still need help, PM me and I'd be happy to go through your config files and help sort the mess out.