Many were still without services today as the bank's servers struggled to cope with the demand for Net transactions.
Services ground to a halt last Wednesday and although they were restored for two days over Easter, they collapsed again today.
The crash coincided with the introduction of online payroll and multipay services, however, the bank denied that that had been the direct cause of the problem.
It is not known how many businesses had had to find alternative methods of paying wages or making other payments in the lead up to Easter.
Individual customers have also been seriously affected.
Users of the online service have been unable to access account details, make transfers, use Bill Pay or make interbank transfers.
Bank of Queensland corporate affair manager Paul Turner said there was nothing fundamentally wrong with the site, but there were difficulties with communications between parts of the site and the bank was working with its outsourcing partner Electronic Data Systems (EDS) to resolve the issues.
"It is not as simple as a bandwidth problem and has taken some time to track down and fix. There is no doubt it is linked to the unprecedented demand for the Internet banking service," said Turner.
He denied that the bank had grossly under-estimated the server capacity it would require when it launched Internet banking nine months ago.
"There have been some teething problems, but there has also been a dramatic increase every month since we began in the number of customers registering to use the service.
"We have gone from zero to 40,000 users in nine months and prior to that there had been little indication from customers that it would be this popular".
Turner said the service was being upgraded to cope with the demand and it was hoped that full services would be restored by later today. In the meantime he suggested customers delay any unnecessary transactions until after hours, when traffic was not usually so heavy.
The Bank of Queensland's problems follow similar difficulties and service collapses suffered by Westpac and National Australia Bank last year as the popularity of Internet banking continues to soar.
Looks like it has failed again under the weight of its takeover of Home Building Society in WA. So much for the advertising of 24 7 service and "We expect this to be a smooth transition"