Actually, I encounter this problem some months ago, but I just post it now, because I've seen many other problems have been posted here.
I use [sweetcaptcha_contact_form] shortcode and I like it.
It works here:
There's no problem on that page, and the contact form was successfully submitted.
But when I edit that page, it conflicts with Facebook Publisher feature of Simple Facebook Connect (SFC) plugin. Because of this error, some other settings can't be displayed.
You can see this:
Fatal error: Call to undefined function sweetcaptcha_shortcode()
I don't know, maybe SFC is not the only plugin that has a conflict with the shortcode. I have some other plugins that add extra settings to the Edit Post/Page. All of them are not displayed until I remove the shortcode and click Update button.