.net Framework 3.5 Fix Jun 2026

Alongside WPF, .NET 3.5 was the primary runtime for . Though Silverlight is now defunct (a victim of the HTML5 revolution), it was once the "Flash killer" that powered rich internet applications. Understanding 3.5 is essential for understanding the Silverlight era.

Because it is not fully compatible with newer versions (like 4.x), .NET 3.5 must be installed separately. On modern Windows (10/11), it is an optional feature: .NET Framework 3.5

While no one should start a new greenfield project on .NET 3.5 today, knowing how to enable it via Windows Features, repair it with DISM, and secure it with modern policies will save countless hours of frustration. The framework may be from 2007, but for many critical systems, it remains as essential as the day it launched. Alongside WPF,

Install the Visual C++ Redistributables for Visual Studio 2005, 2008, and 2010. Also, ensure no custom .config file is forcing a newer runtime version. Because it is not fully compatible with newer

There is significant confusion about whether .NET Framework 3.5 can run alongside .NET 4.8. The answer is . They are side-by-side compatible installations. An application targeting .NET 2.0 will use the CLR 2.0 provided by the .NET 3.5 installation. An application targeting .NET 4.8 will use the CLR 4.0.