Question:

Why does a user receive the error Picklist value cannot be deleted because it is in use when making an object picklist value inactive in Vault?

Answer:

If a picklist value is referenced in a workflow step(s), the user will receive the error below when attempting to make the referenced picklist value inactive. This reference in the workflow(s) will need to be removed to proceed with inactivating the picklist value.

Related Documentation:

Vault Help Documentation: N/A