This sounds similar to the problem I had a few months back.
I was trying varous settings in Document Environments area
in Tools - Options - General - Document - Linked Document Localization window.
We don't have Smarteam either, so I DEACTIVATED PDM Reconciliator, Catalog & Startup, Smartteam and ENOVIA VPM options. (Seems to help larger assembly models to open quicker)
I then opened an Assembly model (Product), and all the Part models inside the Assembly were not loaded and I got a similar error to yours.
I then went back to the Document settings and ACTIVATED
the previous settings, re-opened the Assembly model and
all the Parts were there and had no error.
Hope this helps,
Jakey