I had the same issue, i succeed with Kaldraydis post, but i could not install. To solve the issue i had to start the Windows Secondary Logon service, just as MnkyMjk mentioned. Here is the guide:
The Windows Secondary Logon service is used to enable to disable the starting of processes under alternate credentials, and this service needs to be enabled and running for Agent to not only be able to do its thing but to even just start. To make sure that the Secondary Logon service is enabled and running, you need to:
- Press the Windows Logo key + R to open a Run
- Type services. msc into the Run dialog and press Enter to launch the Services Manager .
- Scroll down through the list of services, locate the Secondary Logon service and double-click on it.
- Open the dropdown menu in front of Startup type: and click on and select Automatic .
- Make sure that the service is running. If the service is not running, click on Start . If the service is running, simply skip this step.
- Click on Apply .
- Click on OK .
- Close the Services Manager and restart your computer.
When the computer boots up, check to see whether or not the Battle. net Agent ’s ability to successfully download data and/or install game files has been restored.
Source: appuals. com/fix-battle-net-issues-cant-download-data-or-install-game-files