Server - Internal server error on item spawning

[SimonsPure]

So I'm a little new to this but....

Whenever I try to spawn an item whilst on my server I get kicked out with an "Internal server error" message.

I brought the world from a vanilla server.

If I'm doing something stupid, please point it out without being too condescending.

Thanks in advance!

[Pilchard123]

Did you try to spawn it from the vanilla creative item list? That doesn't work with mods for some reason, so you'll have to use NEI.

[SimonsPure]

I tried using the center set of items (Vanilla) and the ones on the right (Which I assume are NEI).

[KakerMix]

Its a bug with NEI and creative mode. Don't touch your center creative window, or item bar on the bottom. Touching those in creative will crash you. Always.