This error didn't make the Asset Manager unusable, it just broke some thumbnails.
As I suspected this is a result of having created an image space but not having permission to view any forums that make up that space or the forums that are part of the space are not in the vBulletin forum cache, as discussed in the previous report. I applied the same fix I suggested in the other report (which you said didn't work on 3.0.11) and it's working now on 3.0.12. Marking as a duplicate.
You also have some issues with the attachment javascript. Try redownloading the VaultWiki ZIP and replacing the /clientscript folder.