The reason a new application throws this 'Compiler Error' is because the VS.NET Designer does not add the references to the other assemblies that are used.
Dragging-and-dropping the GridGroupingControl to a WebForm, adds references to the following assemblies in addition to the Syncfusion.Grid.Grouping.Web to your project:
This is because the grid uses certain types defined in the above assemblies. For the same reason make sure to add the to the aspx file, just so the designer will find the types in these assemblies when referenced.
Note that you might have to change the version number in the tags to whatever version you are linking to.
This page will automatically be redirected to the sign-in page in 10 seconds.