Amazon.com’s cloud-computing service was beset by “high error rates” on parts of its S3 data-storage system, disrupting many internet sites and mobile applications that rely on the company for their online presences. “We are working hard at repairing S3, believe we understand root cause, and are working on implementing what we believe will remediate the issue,” the company said on its website at 11:35 a.m. in Seattle.