CheckFree said it has identified and corrected the root cause of the system error that led some users of its e-billing/payment service last week to experience intermittent problems accessing and using the system. The error affected consumers who both attempted to access electronic billing and payment services through Intuit's 'Quicken' or Microsoft's 'Money' software, and who bank at financial institutions that process transactions on the firm's newest processing system, 'Genesis'. CheckFree traced the problem to application code in its middleware, which affected entry to the 'Genesis' system. The company says such problems are extremely difficult to detect in simulated stress testing and are not unusual as growth occurs. CheckFree acknowledge the problem could have affected up to about 20% of its 2.8 million subscribers. The glitch first made its appearance last Monday and was resolved by Friday. The e-bill company says it is preparing a thorough internal review of the system interruption and restoration events. For more information: www.checkfree.com.