Controls in this category are unavailable for the .NET Framework 4 Client Profile. To change this setting, open the Project Properties window.
Resolving “Controls in this category are unavailable for the .NET Framework 4 Client Profile”
Syncfusion controls are available for .NET Framework 4.0. By default, .NET 4.0 Client Profile is selected as the target framework in the VS2010 environment. To resolve the “Controls in this category are unavailable for the .NET Framework 4 Client Profile” error, the target framework must be changed to .NET Framework 4.0. Navigate to the Project toolbar item, and then select Properties (Application properties). In the Application tab, change the Target framework to .NET Framework 4.
In the Visual Studio toolbox, you should now be able to use the controls from the VS toolbox.