Knife vault admin issues

I am working on chef windows environment. I am having some problem in using the knife vault commands.
The user to which admin access to the vault was given, is now deleted and no more in use. Now, i am unable to add any other user to access the vault.

I get the following error when i try refreshing the vault(as recommended) or add new admin.
ERROR: ChefVault::Exceptions::SecretDecryption: ..../.... is not encrypted with your public key. Contact an administrator of the vault item to encrypt for you!

What should I do in this case?