Attachment File Not Found
The attachment you were trying to download could not be found in the attachment file store. Either the file has been removed manually or there was an error in removing the record of the attachment from Confluence.
If this attachment is no longer required you can remove it from Confluence on the attachments page. Otherwise, you will need to attach a new copy.
Please check your Attachment storage from below given location.
Administrator console > Attachment Storage (Under Configuration Column on left side of your screen)
Please point Attachment Storage to In Confluence's configured database by selecting radio button.