This error message can occur when a target file or folder has been deleted, moved, or renamed, between the time the sync started and the time that the file is reached.

For example, a sync is processing 1000 files. The sync generates a list of the names of the 1000 files and begins processing them. However, file number 999 is renamed during the processing. When the sync reaches file 999 it will not find it as its name has changed and an error is logged. A subsequent sync should pick up the renamed file, assuming it isn't renamed, deleted, or moved again.