Form processing error

I have created a form, made it a server connect form, added the necessary set up mailer, send mail, saved the action file

When I test the form by filling in the fields and hit send the form is emailed successfully
BUT the webpage goes to what looks like an error page showing

I have removed the form I created and inserted a form block, saved it all etc but still get the same result.

What am I doing wrong?

Screenshot 2019-06-18 at 10.51.54.png1412×186 18.5 KB