The deal is, with error codes 0x800B0100 and 0x800F0900 (effectively the same problem with the same fix of repairing corrupt .cat, .mum. and .manifest files in SURT log) sometimes (sporadically with no known precise causes/correlations) the updates which were corrupt or have in the past failed will continue to fail through the Windows Update interface with error code 0x8024200D (ERROR_DS_ATTRIBUTE_OR_VALUE_EXISTS). Fortunately, the fix is simply: install manually from microsoft.com.