JaneW on "[Plugin: iThemes Security (formerly Better WP Security)] Internal Server Error"

I have been receiving random Internal Server Error messages since installing this plugin. It never happened before but now it seems to happen quite often. I have only seen it on the backend - such as when I save a post - so I don't know if it's affecting the frontend at all.
Doesn't matter, I need it to stop doing that, it's annoying.
I haven't lost anything - I can always just reload and it takes me back to my post and it has saved - but it's tedious.
I assume it's something I have set incorrectly in the plugin, but I wouldn't have a single clue as to where to start looking.
I suppose I could just reset everything to default and start from scratch, but wouldn't it be nicer if you just told me where to start looking? :)
Thanks!

https://wordpress.org/plugins/better-wp-security/