Open or Command Prompt as Administrator .
Run the installation again via Server Manager or DISM without the /Source parameter. Troubleshooting Can not install dotNet 3,5 on Windows Server 2012R2 Open or Command Prompt as Administrator
While Windows Server 2012 R2 is a legacy operating system, .NET 3.5 remains a critical dependency for many enterprise applications. Utilizing the microsoft-windows-netfx3-ondemand-package.cab via DISM remains the "Gold Standard" for ensuring a clean, offline installation on new server deployments. you have three reliable installation methods.
: Insert or mount your Windows Server 2012 R2 ISO. Open or Command Prompt as Administrator
Once you have the microsoftwindowsnetfx3ondemandpackagecab stored locally (e.g., C:\Temp\NetFX3\ ), you have three reliable installation methods.