This functionality was never coded explicitly in the 10Tec ImageList OCX. It's a quirk in MS Access and works only in this environment for the Classic ImageList created with VB6. The new Modern ImageList was created with twinBASIC, and this shortcut to open the property pages dialog no longer works.
Of course, this dialog is present in the Modern Edition of ImageList. To open it, click the ellipsis button in the value of the Custom property in the Properties pane when the ImageList is selected on the form.
In future releases, a corresponding command to open the dialog will be added to the context menu of the control on the form.