While trying to delete Off-Page Reference Icon, the below error is observed:
The off-page reference icon is a special purpose topology icon. The off-page reference icon represents a device that is directly connected to a device in the current view but which is modeled in another layer. The following icon shows an example of an off-page reference icon:
The above icon cannot be deleted
You could make the "Off Page Reference Models" not visible as below:
From the OneClick Console, click on > View > Preferences > Topology Tab > Show Off Page References > Set "Specifies whether or not Off Page Reference Models are visible" to No > If you want the changes to be Permanent, ensure "Make Changes Permanent" is check marked (default) > Click on Apply > Click on Ok
For further information, please refer the below links: