Box Sync 4.0 provides detailed user notifications if there an issue syncing a file or folder.
Box Sync requires a temp folder to store temporary information. The location for this folder must be on the same volume as your Box Sync folder. If the Box Sync folder is located on another volume, Box Sync attempts creating a temp folder as a sibling of the Box Sync folder. For example, if the Box Sync folder is: X:\Stuff\Box Sync, then Box Sync attempts creating a temp folder under X:\Stuff.
If your account does not have permission to access this location, then Box Sync cannot create a temp folder and issues this problem notification.
All devices with Box Sync installed.
For Box Sync to create a temp folder, you must have permission to create folders at the parent level of the Box Sync folder (For example, at the X:\Stuff level in the example above). If you do not have the required permission to create folders, contact your system administrator. Once you have the required permission to create a folder, restart Box Sync.