This is a troubleshooting trick that Microsoft Support themselves use, which gets rid of an entire class of problems with Microsoft Update.
If you have problems with Microsoft/Windows Update, you might want to try this to “refresh” its cache/memory. You have nothing to lose (except some time and bandwidth):
Step 1: Rename the Windows Update Softwaredistribution folder
This issue may occur if the Windows Update Software distribution folder has been corrupted. We can refer to the following steps to rename this folder. Please note that the folder will be re-created the next time we visit the Windows Update site.
1. Close all the open windows.
2. Click “Start”, click “All programs”, and click “Accessories”.
3. Right-click “Command Prompt”, and click “Run as administrator”.
4. In the “Administrator: Command Prompt” window, type in “net stop WuAuServ” (without the quotes) and press Enter.
Note: Please look at the cmd window and make sure it says that it was successfully stopped before we try to rename the folder. However, if it fails, please let me know before performing any further steps and include any error messages you may have received when it failed.
5. Click “Start”, in the “Start Search” box, type in “%windir%” (without the quotes) and press Enter.
6. In the opened folder, look for the folder named “SoftwareDistribution”.
7. Right-click on the folder, select “Rename” and type “SDold” (without the quotes) to rename this folder.
8. Still in “Administrator: Command Prompt” window, type the command “net start WuAuServ” (without the quotes) in the opened window to restart the Windows Updates service.
Note: Please look at the cmd window and make sure it says that it was successfully started.
This was taken straight from https://apapadop.wordpress.com/2010/07/03/a-usability-case-study-microsoft-online-assisted-support/