Anytime I try to add any item from any pack to my inventory, I get disconnected from my server. If I can't find a solution, I can do without the mod. I was adding it for decorating my streets anyway. But I would like to find a solution because it's a cool mod. I do not have this issue in single player with the exception of one pack that I removed.

This is what the console says right before/as I get disconnected:

[16:04:50] [Server thread/INFO] [minecraft/NetHandlerPlayServer]: THASSELHOFF lost connection: Internal Exception: io.netty.handler.codec.DecoderException: java.io.IOException: Packet 0/27 (CPacketCreativeInventoryAction) was larger than I expected, found 4 bytes extra whilst reading packet 27

So sorry. I'm an idiot and accidentally placed the mods in the wrong folder for the server but didn't think anything of it because it showed up on my screen in game.