The registration process requires two onchain transactions (Commit + Register) to be completed within 24 hours of another.

The "CommitmentTooOld" error means the second Registration transaction is being attempted more than 24 hours after the initial Commit transaction. Registration will therefore need to be restarted.

Solution:

To begin again: clear your browser cache & cookies for the Manager App (app.ens.domains), reconnect your wallet, and restart the registration process.