The document “Main.storyboard” requires Xcode 8.0 or later.
This version does not support documents saved in the Xcode 8 format. Open this document with Xcode 8.0 or later.

如下圖所示：

解決方法是在工程中選擇 Main.storyboard 右鍵菜單點擊 Open As -> Source Code ，如下圖所示：

刪除這句：

<capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>

然後選擇 Main.storyboard 右鍵菜單點擊 Open As -> Interface Builder，就能重新加載看到設計界面了。

原文地址：https://www.exchen.net/main-storyboard-requires-xcode-8-0-or-later.html

The document “Main.storyboard” requires Xcode 8.0