It seems that Windows Server 2003 needs a server-wide solution and all hotfixes didn't work, so it must be done manually.
- Edit C:\WINDOWS\Microsoft.NET\Framework\v4.0.30319\Config\Browsers and add the browser definition in this answer https://stackoverflow.com/a/19203518/1297563
- Run c:\WINDOWS\Microsoft.NET\Framework\v4.0.30319\aspnet_regbrowsers.exe -i
- Restart IIS