An unknown error has occurred.是什麼意思

An unknown error has occurred.是發生了未知錯誤的意思，例如

As many people want to access the website to book for an vaccine appointment， website can't copy， then there message will be seen :an unknown error has occurred. 由於很多人想訪問網站進行疫苗預約，網站無法複製，然後會看到消息：發生未知錯誤。