I am also having trouble but it says 'the transmitter CRA account number given in the attached T619 electronic transmittal record does not match the account number you used to sign in'.  I called CRA and they said my software (QuickBooks) should be updated so I can enter my account number as MM555555 is no longer accepted (nor is 00000).  But there is nowhere to update this information.  Is there an update coming?