So I'm making weapons and armour and whenever I try using the console in game with player.equipitem (ID) 1 I get that message, even though the ID is correct and my plugin is saved I get this message. I've got no other mods on to conflict with it and I'm stumped as to why this is happening. Even the wiki says I'm doing everything right but for some reason the ObjectID can't be found.

Any ideas?

Just a guess, seeing as you said you're not using other mods.

Try changing the first 2 digits of the ID in the console to 02.

This solution worked for me, but can anyone explain why the name of the new item can't be used (the CK tutorial refers to the new item by name) and why changing the digits to '02' would work? Am I missing some setting somewhere?

The prefix refers to the mod order. Vanilla objects are contained in the First file loaded - Skyrim.ESM This means they have prefixes of 00.

The first mod you load will be the 2nd in order, and so all objects of that mod will have the prefix 01. It's all a system to avoid duplicate filenames.

02 is the Mod Index of your file. 00 is always Skyrim.esm, usually player plugins start at 01 and move up hexadecimally, however Skyrim now has a hidden Update.esm file which loads too. This means player loaded mods start at 02, and progressively increase depending on what mod is loaded in what order (02, 03, 04, 05, 06, 07, 08, 09, A, B etc).

And Object IDs can never be used in the console. You have to use the formIDs.

Actually now 01 is always the Update.esm so first mod is going to be 02 !! (00 is oblivion.esm)