Hi Diego,
This means you failed to sign the transaction with one or more of skeys corresponding to a vkey used in the transaction.
For stake pool registration, you will want to sign the transaction with skeys for the payment address paying for the transaction, all stake address being assigned either as rewards account or owner account (each delegation certificate), and the pool cold key.
This is an example of how to sign a pool registration having separate rewards and pledge addresses:
cardano-cli shelley transaction sign /
–tx-body-file pooltx.raw /
–signing-key-file payment.skey /
–signing-key-file stake.skey /
–signing-key-file pledge-stake.skey /
–signing-key-file cold.skey /
–mainnet /
–out-file pooltx.signed
Your friend, FROG