Hello Michel,

This error happens when you have two versions of a DLL that use the same namespaces and class names. You can use external assembly alias to wrap the namespaces from each assembly inside root-level namespaces, which enables them to be used in the same file. So, first you have to specify the ‘Aliases’ property of the .dll references in the following way:

1. In Visual Studio Solution Explorer, open References folder
2. Select Infragistics4.Shared.v16.2 reference and right-click on it, select ‘Properties’
3. Enter alias value in "Aliases" property, for example ‘WinForms’
4. Select InfragisticsWPF4.v16.2 reference and right-click on it, select ‘Properties’
5. Enter alias value in "Aliases" property, for example ‘WPF’

To use the aliases from within a program, reference them by using the extern keyword. Note that the extern aliases should be placed on top of all usings:

extern alias WinForms;

extern alias WPF;
using System.Windows.Forms;
...

Then, in code you specify the alias namespace and class you would like to use the following way:

WinForms.Infragistics.Shared.ResourceCustomizer rc;
WPF.Infragistics.Shared.ResourceCustomizer rc1;

This way the types from each assembly can be referred to without ambiguity by using their fully qualified name, rooted in the appropriate namespace-alias. The rc would be the ResourceCustomizer from Infragistics4.Shared.v16.2
.dll and rc1 would be the ResourceCustomizer from InfragisticsWPF4.v16.2.

In your case, I guess you would need only the WinForms ResourceCustomizer rc as you are using the WinForms UltraGrid.