Starting with version 2.9.1 this error is deprecated. More detailed error messages about .sync/ID file are described here.
All agents in Synchronization job and destination agents in Distribution & Consolidation jobs create .sync folder in the root of the directory chosen for this job. It's a hidden folder and it contains the following:
- ID file (folder identifier, by which the agent recognizes the folder it needs to sync);
- IgnoreList (a test document for ignoring and whitelisting files);
- StreamsList (a whitelist for files alternate streams and extended attributes);
- Archive folder (directory that stores deleted files and their old versions).
Deletion or corruption of the whole .sync folder or ID file results in "Cannot identify destination folder". To fix this error remove the agent from this job and add it back. For Distribution & Consolidation jobs it's required that job is restarted. 