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