A technical problem blocked account access for holders of one of the most popular prepaid cards, RushCard. RushCard’s problems started over the Columbus Day weekend, when it switched from one processing technology provider to another. Customers reported problems gaining access to their funds, swamping the company’s telephone service center and website. RushCard, founded in 2003 by the hip-hop impresario Russell Simmons, said on Tuesday that the problem had been mostly fixed. But thousands continued to experience difficulties. RushCard has been criticized previously for charging its largely unbanked customer base substantial fees for ATM withdrawals and for each point-of-sale transaction.