I'd use the style listed under "Validation states" at http://twitter.github.io/bootstrap/base-css.html#forms. That'll require something like:

```html
<td class="control-group error">
    <input type="text" id="inputError">
    <span class="help-inline">Must begin with a letter and contain only letters, numbers, '-', and '_'</span>
</td>
```

Then to toggle it on and off you not only have to show and hide the error message, but you also have to add and remove the `error` class to `format_warning`'s `parent()`.

I'd also get rid of "Invalid Property Name", because the red outline around the box will communicate that.