When deleting certain unwanted backup files, it is very normal to eventually receive the dialog with the message:

Failed to delete files on DriveHQ.com

From that point, it is not possible to delete any file until I logoff from the service, then logon, then try again until it works.

Any reason for this?

I just discovered that one of the folders was actually deleted, but still displayed in the File Manager.  Then, when refreshing the manager, the folder disappeared.  I guess that it was deleted after all.

Please note for best performance and minimize the load on server, DriveHQ FileManager has used very extensive caching. If you delete file or folders from another computer, or if you delete using FTP or Web browser, FileManager doesn't automatically refresh the folder/file list. You need to explicitly refresh the folder/file list. When you try to delete a file/folder that has already been deleted, FileManager might have a bug, which we will double check.