All of my security updates are failing with the 800B0100 error code and I just noticed that this has been occuring since 11/15 when my computer downloaded SP1 (successfully). Other downloads are working (eg, Hotfix for Windows KB947821 downloaded successfully on 12/5). It appears that only the security updates are failing. My computer was bought new on 10/31/11 and has Win 7 Home Premium x64. The initial security updates DID work but occassionally failed. After the SP1 download, none are working. I have run the System Update Readiness Tool. Attached are the CHECKSUR log and the CBS log. I would greatly appreciate any help!