Thanks for your response. I voided the transaction, set up a new password on the EFTPS website, then went back to QB to resubmit the payment. I clicked off 'remember my password' entered the new password along with my pin but shortly afterwards I received the notification the the payment was rejected - this time by an authentication error. 
I'd welcome your thoughts on this. 

In the meantime I went ahead and submitted my payments directly at the EFTPS website.