You need to set up a valid path for the RDB Logs through Access RDB:
Close RDB Sync.
In RDB, Click Options and then click User Preferences.
Click Error Handling.
Make sure that the Log Errors box is ticked.
Ensure that the path in the Store Folder is accessible:
Click Browse.
Set to accessible path (e.g. under user documents).
Tick the Show detailed error messages box.
Click Save and Close.
Restart the RDB Sync Application.