ITrack/Quickbooks/Object specified in the request cannot be found

Object "[some Quickbooks ID]" specified in the request cannot be found. QuickBooks error message: Invalid argument. The specified record does not exist in the list. Code: 3120.

Cause

This usually happens because something became unsynced between ITrack and Quickbooks (some object was altered in Quickbooks in such a way that Quickbooks gave it a new ID that ITrack doesn't know about).

Solution

Make sure that all of the objects on the thing you are trying to push (not the thing you are trying to push itself) are synced with Quickbooks.

Do this by finding them in the appropriate list, double-clicking on them, and selecting the correct object in Quickbooks.