OK I have fixed it!!!
For anyone else with the same issue I had some images I had added to the page that started with [url-base]. I have removed this from the links and the page now works fine.
$allowed_attr = $allowed_html[strtolower( $element )];
its fixed. I deleted the old ninja forms folder and then copied in the new one and it now works.
Thanks
that is the version I downloaded
