Modded Items on Forge server vanishing

So, I recently got a hang of port forwarding and made my own Minecraft server, I have 4 servers, a Vanilla Creative server, A Cauldron server , A Forge Server and a Pixelmon Server, (They are all private)

On the Cauldron Server, every time I tried to craft a modded item, it simply would not allow me, when I tried to drag it into my inventory, it just went back into the box
So, I wondered if this happened to all modded items, and sure enough, I could not.
I could get the items from creative, and when I went back into survival and tried to use them they disappeared, and in single player the mods worked fine, when I tried to get them from NEI but it just said "The ID <Item ID> is invalid" I tried to make a forge server and thought cauldron was the problem, and the exact same thing happened

Something to note, the servers work fine without mods, and people can join the modded servers, just they cant use the mods

Please Help