Hello,

Thank you for contacting Infragistics Developer Support.
If I understand correctly you want if some item is selected others to not be, please let me know if I am wrong. To do so you can use the selectionChanging event. If you return false the selection will be cancelled. In the ui variable you can select all candidate selection items with ui.items. Then check if there are any selected items and they are not from the restricted list. 

$combo.igCombo({
    dataSource: colors,
    textKey: "Name",
    multiSelection: "onWithCheckboxes",
    valueKey: "Name",
    width: "200px",
    autoComplete: true,
    selectionChanging: function (evt, ui) {
        if (ui.items && selectedItemsContain(ui.items, ['Red', 'Brown'])) {
            return false;
        }                        
    }
});

I have attached a with the implementation of the selectedItemsContain. If you have any additional questions please let me know.

Hello Gloria,

Have you been able to resolve the issue?
If you have any concerns or questions, please feel free to contact me, I will be glad to help you.
Thank you for choosing Infragistics components!