Unknown Object error is issued in the following situations:
Unknown object '<Image or Resource>' used in '<Theme or Block>' Style Sheet.
The Style Sheet of the Theme or Block contains a reference to an unknown image or resource.
Open the Theme or Block Style Sheet and fix the reference to the image or resource, or add the necessary image and resource to your module.
Object '<Resource>' used in '<Theme or Block>' Style Sheet is not being deployed.
The Style Sheet of the Theme or Block contains a reference to a resource that has the property Deploy Action set to
Set the property Deploy Action of the resource to
Deploy to Target Directory.
Double-click on the error line to take you directly to the source of the error.