这是一个安装了 OmniMarkupPreviewer 插件后，又缺少了依赖（比如重装系统）后才会出现的问题。见这篇文章。

错误现象：

Error: 404 Not Found

Quick Fix 1: Remove Strikethrough Extension

Sublime Text > Preferences > Package Settings > OmniMarkupPreviewer > Settings - User
paste the following to remove the strikeout package.

{
    "renderer_options-MarkdownRenderer": {
        "extensions": ["tables", "fenced_code", "codehilite"]
    }
}

Quick Fix 2: Fix the Strikethrough Extension (if you need it)

Find the python-markdown sublime package.

On the Mac: subl "/Users/<username>/Library/Application Support/Sublime Text 3/Packages/OmniMarkupPreviewer/OmniMarkupLib/Renderers/libs/mdx_strikeout.py"

Replace the makeExtension() method with the following:

def makeExtension(*args, **kwargs):
    return StrikeoutExtension(*args, **kwargs)

Save, quit and reload Sublime Text.