|Windows 7 - 64bit|
After reading various fixes from numerous websites this is what I've learned. My problem probably started 2 months ago or better. The red X icon appeared in my taskbar and no matter how many times I tried updating Security Essentials manually it would go through the motions, downloading definitions and trying to apply them. It would then give me an error message with a code (sorry, I just "fixed" it for the 2nd time and forgot to write down or take a snapshot of the error code). What I found online made references to issues with CCleaner, which I do use occasionally but not often. It cleans out a temp folder that MSE uses and after the deletion of the content within this folder, MSE refuses to update automatically or forcibly. The only fix that worked for me is this file, "tweaking.com_windows_repair_aio_setup.exe", Tweaking.com - Windows Repair 1.9.2. After installing the program I skipped to the last tab, "Start Repairs" and clicked "Start". (I did use the "Step 4 (optional)" tab to create a restore point and registry backup.) I personally chose to unclick the Host File (bc I use a modified Host File), and ran the program letting it reboot Windows after it was finished. After the reboot, Security Essentials worked again. Recently, using CCleaner again, I ran into the same problem. Using the Tweaking.com - Windows Repair 1.9.2 tool again, I had no issues after reboot. I hope this helps. Just copy and paste the "tweaking.com_windows_repair_aio_setup.exe" into your favorite search engine and the file will be found available from various sources.