joomla contact form error 500

The Joomla contact form has been known to present users with an "error 500" message, particularly when using SEF plugins such as Artio.

If you have a missing "option" field in your contact form, you'll have to add it into your contact form template for Joomla.

Edit the file: templates/<your_template>/html/com_contact/contact/default_form.php

Add this:
<input type="hidden" name="option" value="com_contact" />

right before this:
<input type="hidden" name="view" value="contact" />

Templates should include this by default, but sometimes it's left out. Without the hidden option field you're going to run into error 500 problems.