In the GUI no armor/weapon/tool can be placed in the slot for enchanting. However, anything can be put in the slots for items. Reloading map/server/game doesn't help. No crushes but it is unusable.

were the items enchanted, when you tried to put them in?

No, they weren't. Checked now with enchanted items - works correctly with them. Is this my fault and unenchanted items are not suppozed to work?

The table is only for upgrading existing enchantments, so non enchanted items are not allowed in the first slot