### `\``normalsize` not defined

The LaTeX error:

```The font size command \normalsize is not defined:
there is probably something wrong with the class file.
```

reports something pretty fundamental (document base font size has not been set, something the document class does for you). It can, in principle, be a problem with the document class, but is more often caused by the user forgetting to start their document with a `\``documentclass` command.