If you see an error message where the NAV server or client cannot create an instance of the object, then you may have a security problem.
This problem is not the same as when it cannot load the object. When NAV loads the add-in it only needs read access to the DLL file. However, when it wants to create an instance of it, it needs execute permission as well.
Execute permission is sometimes blocked on code downloaded from the Internet. This is a built in security feature of Windows that blocks all executable content when it is downloaded. This will affect file types such as exe, dll, and chm.
Unblock the file by opening the file properties and select Unblock as shown in the image below.