EllieUpupa on "[Plugin: Contact Form 7] Server Error 500"

Still having this problem!

Upgraded to WP 4.0, CF7 3.9.3

Got WP-Mail-SMTP configured with gmail account, test email works great.

When submitting I get Server error 500:
HTTP/1.0 500 Internal Server Error
Date: Sun, 07 Sep 2014 13:03:22 GMT
Server: Apache
X-Powered-By: PHP/5.4.17
Content-Length: 0
Connection: close
Content-Type: text/html
Pragma: no-cache
Cache-Control: no-store, no-cache, must-revalidate, max-age=0
Expires: Tue, 01 Jan 1971 02:00:00 GMT

Is there anything else I can try/test?

Thanks in advance,

Ellie.