I have been getting this error for weeks in both of my trees. After troubleshooting failed to resolve the issue (including compacting, unlinking, relinking, generating sync error reports), I have been told how to clean boot to delete some files, unlink the trees, then uninstall the program and start over from scratch. So far, I have downloaded my small tree (400 people, 800 records)and was able to sync changes I made a couple of times. I am now in the process of downloading my large tree (16,000 people and 18,000 records). I really hope the error does not come back after all this trouble.