I came here to post about the fix, but i see that Profaitchikenz Haiku above has already mentioned it, thank goodness. Too bad I didn't find this before I spent one of the worst SL days ever trying to ask for help and to fix it myself. All I was finding when I was searching previously was old postings from over 4 years ago. I should have looked in the Most Recent postings, but I thought it was a problem that was just affecting me since I hadn't logged in for a while.
To recap, the sync would never complete, and new items could not be added until it was complete, so it said. Some areas of the interface said I was wearing new attachments, other areas did not, and the Right-Click on Appearance was not there, so it was broken too, and rebake and clear cache and restarts and updates and other viewers and other computers.... none of it worked. So I just kept trying to attach and detach objects, and the popups would say items were not in inventory, even though I could clearly see them in the list (not just links).
I had found two items (hair and shape) that were working, but I could not find ANY hair or eyes that would work. So after fishing around a while, I decided to try over in the Inventory CREATE NEW skin, and that is what FINALLY worked. I then made NEW eyes also, and so the final result was that I now have only those 4 items in use Hair Skin Shape and Eyes, as user Haiku noted above.
Good luck and I hope everyone who has been hit by this breakage will find this thread. And Lindens... Please Stop Releasing Things before you Fully test them! It's not worth $100 a year to spend a whole day trying to fix what I'm paying for you to keep working. Thank you.