Diablo 3 Stucked at ‘Updating Setup Files’ Issues
If you have purchased a digital copy of Diablo 3 and having difficulty running the Diablo 3 Client Download, some will experience some issue stucked or loops on the ‘Updating Setup Files’ screen. Here is the step to fix this Diablo 3 game launcher error.
1. Control Panel > Administrative Tools > Services
2 Scroll down and find “Secondary Logon”
3. Right Click > PropertiesChange it from ‘Disabled’ to ‘Automatic’
4. Run your Diablo 3 setup as administrator (right click on the Diablo 3 client downloader)
Now the launcher will start downloading!
Source : Battle.net forum