This does not inspire confidence

Just tried to transfer some money from one of my bank accounts to the other using St George and got this message:
Your transaction may have been unsuccessful.
Please logout of Internet Banking and login again. Before making this transaction again, please view your transaction history to check if this payment or transfer was processed.
We apologise for any inconvenience caused.

That does not inspire confidence. Your transaction may have been unsuccessful. What kind of computer system can't be sure?