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The electronic system the Small Business Administration is using to set up new coronavirus loans was down much of Monday, according to senior banking executives, making it impossible for many new loans to be guaranteed.

Billions of dollars in loans sought by small businesses trying to pay employees and keep their doors open were on pause as the SBA, supported by the Treasury, grapples with the demand on its system.

There are an estimated 30 million small businesses in America. Many are expected to apply for the program, which offers up to $10 million in loans that can turn into free grants if the businesses follow certain rules, which include using the money primarily for payroll.

Customers walk through the Dupont Circle Market in Washington, DC on April 5, 2020. Daniel Slim / AFP - Getty Images

“E-tran,” the SBA’s proprietary loan guarantee system, has suffered from technical errors, access issues and extreme slowness since the launch of the $349 billion small business rescue effort authorized by Congress, frustrating small business owners looking for a lifeline.

When the system does work, banks say they experience major technical issues and access hurdles. Existing accounts had to be re-authorized and new ones created.

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"Unfortunately, our District Office personnel have absolutely no means to set-up user accounts, unlock user accounts or reset passwords," an SBA regional office said in an email to lenders reviewed by NBC News.

This means that if a bank had only two logins, then only two people could enter data into E-tran.

“We have asked SBA for more information on who they are using & what their plan is for improving access to E-Tran,” tweeted Sen. Marco Rubio (R-FL), chair of the Small Business and Entrepreneurship Committee. “This MUST be corrected ASAP.”

In some instances, E-tran asks for information that is not required in the payment protection plan applications or excludes certain applicants who should be allowed.

In a statement, the SBA expressed confidence in the program’s operation and efficacy.

"The system is up and running. We continue to process, approve and guarantee billions of dollars of loans per hour," Jennifer Kelly, an SBA spokeswoman, said in a statement.

The SBA says it has approved $38 billion in payment protection loans. And some banks, especially smaller community banks, have successfully executed some loans. But that doesn’t mean that there’s been $38 billion deposited in customers’ accounts.

Major banks, adhering to tighter regulations enacted after the 2008 financial crisis, are awaiting final technical guidance from the SBA to begin distributions.

“This is an emergency situation, and when you do things in an emergency situation, it's going to be far less than perfect,” Rubio said on CNBC. “What we want to see is that the number of lenders in the system grows every day, and the number of problems and issues with the program diminishes every single day. So it will get better,” he added. “It has to get better.”

A backup system designed by Amazon Web Services to help relieve some of the pressure has yet to become operational.

Amazon didn’t immediately respond to an NBC News request for comment.