Blizzard have announced they had to temporarily disable the creation of Enchanting Vellums due to a bug.
Vellum (Source)
We’ve temporarily disabled the creation of Enchanting Vellums, while we diagnose and fix a bug.
We hope to develop and deploy the fix in the next 24 hours. Until then, Enchanters can enchant items directly or use existing Enchanting scrolls, they just won’t be able to make new scrolls.
Thank you for your patience and understanding.