UNKNOWN_OBJECT — Error Class OBJECT, code UNKNOWN_OBJECT

The device has no object with the requested type and instance number. Object identifiers are a type plus an instance, and both must match.

Start free BACnet/IP → canonical

Diagnosis

When you hit this

An object instance copied from a sibling controller where the numbering differs.
Points renumbered after a controller reprogram or a firmware update.
Requesting an object that exists on the supervisor but not on the field controller.

Resolution

How to fix it

Read the device's object list
Property 76 (object-list) on the Device object enumerates everything present. Discover rather than assume.
Do not port instance numbers between devices
Two identical rooftop units frequently have different instance numbering.

Normalization

What Forge does about it

This is a configuration or addressing mistake on the wire, upstream of anything Forge sees. Where Forge helps is the step after you fix it: once the point returns data, its vendor tag name maps to a canonical field automatically, so you do not also have to hand-maintain a name table for every point you just re-addressed.