最後找出可能的原因:

遺失名為"iPod touch App Pack 4A93"的認證檔案.位置在:

Windows XP
iPhone: C:\Documents and Settings\[username]\Application Data\Apple Computer\iTunes\iPhone Software Updates
iPod: C:\Documents and Settings\[username]\Application Data\Apple Computer\iTunes\iPod Software Updates
(If you don't see the Application Data folder, you may need to show hidden files.)

Windows Vista
iPhone: C:\Users\[username]\AppData\Roaming\Apple Computer\iTunes\iPhone Software Updates
iPod: C:\Users\[username]\AppData\Roaming\Apple Computer\iTunes\iPod Software Updates

原先購買時的PC有重灌所以遺失,而且在另一台PC進行回覆時沒有該檔案就會有錯誤,然後回覆成為未購買狀態

解決方案:重新申請帳戶名稱購買