This week, "America's Most Convenient Bank" was anything but.

TD Bank's planned integration of Commerce Bancorp's systems, scheduled for last weekend, led to a major technical failure that left customers unable to access some of their money through at least Thursday afternoon.

The breakdown in customer service has loosened TD Bank's grip on Commerce's longtime slogan and tarnished its reputation at a time when consumers are exceptionally intolerant of any problems with financial companies.

"This is a really unfortunate glitch for TD Bank in this time when customers are really looking for reliability," said Trish Dorsey, a senior vice president of financial services brand and communications at TNS Global. "This is a pretty massive thing. It's not five or 10 customers, it's a whole organization's worth of customers seeing themselves in a situation where they can't make their mortgage payments or utility payments or car payments."

The U.S. arm of Toronto-Dominion Bank notified customers last month that some systems would be unavailable last weekend during the integration project.

But many customers, including both former Commerce account holders and former TD Banknorth customers, have reported this week that direct deposits and other electronic transfers have not been credited to their accounts.

"Following the system process over the weekend, we experienced a temporary technical issue that caused intermittent delays in processing some transactions," TD Bank spokeswoman Jennifer Carlson wrote in an e-mail Thursday.

The systems problem was compounded, both by its timing, coming at the end of the month when many people get paid, and by TD Bank's inability to handle numerous complaints.

"TD Bank has nurtured a reputation for being not only convenient but also very personal in its approach," said Campbell Edlund, the president of the consulting firm EMI Strategic Marketing Inc. "They may have set themselves a bar that's higher than others with respect to their customer service, and that makes it more challenging when mistakes happen."

Multiple calls to the company's toll-free service numbers would not go through Thursday, and consumers who visited TD Bank branches faced long lines.

On Thursday, it seemed that the best way to reach a customer service representative was through Twitter Inc., where the "Ask_TDBank" team used the microblogging site to apologize to depositors, often with a generic response: "We're sorry processing was delayed & inconvenienced you. Thank you for your patience. We will work to regain your confidence."

Such integration projects are always complex, and complications are not unusual as banks link their systems in the wake of mergers or consolidations. But a glitch of this magnitude is close to a worst-case scenario, said Bart Narter, a senior vice president in the banking group of Boston market research firm Celent.

"Whether you're doing a bank merger or not, every bank [chief information officer's] worst nightmare is not having the batch finished on time. The probability of you having that problem when you double the size of the bank is much, much higher," he said.

"To have four days of nonfully functioning core systems is a pretty big deal," Narter said. "These things at banks these sizes are very rare. A four-day one is a once-a-decade thing."

The incident comes as popular opinion about the banking industry is deeply negative, and is especially unfortunate for TD Bank, which lost the right to hold onto the Commerce name but has tried to retain its well-established reputation for customer service.

When problems of this scale occur, that's "a real call for the bank to be superproactive about reaching out to customers and reassuring them," Dorsey said. "You'll see some churn."

TD Bank's spokeswoman Carlson wrote, "We are working nonstop to resolve this issue." She said the bank anticipated that current account balances would be available Thursday afternoon, and the company "will reverse fees, charges or interest incurred."

But Thursday, many TD Bank customers — even those who reached a customer service representative — were not appeased. "Things I can't do today because of #TDBank: pay rent, pay credit card, pay my student loans, buy groceries... THANKS! I miss commerce!," was one of many frustrated comments posted on Twitter.

And a TD Bank branch in Manhattan was filled with about 30 customers Thursday morning, including seven in a special line set up just to handle direct deposit problems. One man in that line — a Wall Street attorney who declined to give his name — said that when he called the branch, he was told he would have to come in to present proof of his regular direct deposit from his employer.

"My direct deposit wasn't going through. My mortgage is due today, I have other bills due," said the attorney, who had been a TD Banknorth customer.

When asked if he would stick with TD Bank, he hesitated. "I don't know," he said. "They merged with Commerce and became completely unwieldy."