ContactForm error on send I am having problems with the ContactForm plugin. It stopped sending mails.
I'm getting following error after submitting "Could not instantiate mail function." 

PHPMail should be working.
I checked with a simple php outside of craft. Also the sendmail option in ContactForm does not work.

I don't now when it stopped working. I thought when I added a second locale, so I added a new test single including a from with only one locale. But that single cannot send the form, too.

Craft Pro 2.3.2626
ContactFrom 1.4
It definitely sounds like whatever mail method you're using isn't configured properly (phpmail or sendmail).  Try swapping to a proper SMTP server and see if that helps or a transactional email provider like Mandrill (https://mandrill.com/) and see if that helps.