frontend output is form code

What other plugins do you use on the site?

Quite a few…

Select Contact Form 7
Contact Form 7
Settings | Deactivate | Edit
Just another contact form plugin. Simple but flexible.

Version 4.9.1 | By Takayuki Miyoshi | View details
Select Duplicate Page
Duplicate Page
Settings | Donate | Deactivate | Edit
Duplicate Posts, Pages and Custom Posts using single click.

Version 2.3 | By mndpsingh287 | View details
Select Email Templates
Email Templates
Deactivate | Edit
Beautify WordPress default emails

Version 1.2 | By Damian Logghe | View details
Select Flamingo
Flamingo
Deactivate | Edit
A trustworthy message storage plugin for Contact Form 7.

Version 1.7 | By Takayuki Miyoshi | View details
Select Keyword to URL
Keyword to URL
Deactivate | Edit
The plugin allows administrators to build and save a table of keywords and URLs. Once saved any post (or page) that has the keyword will now show that word (or phrase) as a link.

Version 1.5 | View details
Select Limit Login Attempts
Limit Login Attempts
Deactivate | Edit
Limit rate of login attempts, including by way of cookies, for each IP.

Version 1.7.1 | By Johan Eenfeldt | View details
Select MailChimp
MailChimp
Settings | Deactivate | Edit
The MailChimp plugin allows you to quickly and easily add a signup form for your MailChimp list.

Version 1.5.7 | By MailChimp | View details
Select One-Click Child Theme
One-Click Child Theme
Deactivate | Edit
Easily child theme any theme from wp-admin wp-admin without going into shell or using FTP.

Version 1.6 | By tychay | View details
Select Open external links in a new window
Open external links in a new window
Deactivate | Edit | Settings
Opens all external links in a new window. XHTML Strict compliant and search engine optimized (SEO).

Version 1.3.2 | By Kristian Risager Larsen | View details
Select Participant Login
Participant Login
Deactivate | Edit
adds a username/password login to edit a Participants Database record

Version 1.9.10 | By xn*au webdesign | Visit plugin site | Support | Check for updates
Select Participants Database
Participants Database
Deactivate | Edit | Settings
Plugin for managing a database of participants, members or volunteers

Version 1.7.6.1 | By xn*au webdesign | View details
Select Participants Database Chosen Dropdown Element
Participants Database Chosen Dropdown Element
Activate | Edit | Delete
adds a chosen-enabled multiselect dropdown form element to Participants Database

Version 1.5.6 | By Roland Barker, xnau webdesign | Visit plugin site
Select Participants Database Combination Multi Search
Participants Database Combination Multi Search
Deactivate | Edit
add multiple-field search, plus text search to Participants Database List Display

Version 1.10 | By xn*au webdesign | Visit plugin site | Support | Check for updates
Select Participants Database Datepicker
Participants Database Datepicker
Deactivate | Edit
add a jQuery datepicker to all date fields in Participants Database forms

Version 1.2.4 | By xn*au webdesign | Visit plugin site | Support | Check for updates
Select Participants Database Email Expansion Kit
Participants Database Email Expansion Kit
Deactivate | Edit
provides new email actions and defines email templates

Version 1.8.8 | By xn*au webdesign | Visit plugin site | Support | Check for updates
Select Participants Database Field Group Tabs
Participants Database Field Group Tabs
Deactivate | Edit
Creates a tabbed interface for Participants Database field groups

Version 1.8.3 | By xn*au webdesign | Visit plugin site | Support | Check for updates
Select Participants Database HTML5 Form Elements
Participants Database HTML5 Form Elements
Deactivate | Edit
Adds HTML5 special input types

Version 1.4 | By xn*au webdesign | Visit plugin site | Support | Check for updates
Select Participants Database Permalinks
Participants Database Permalinks
Deactivate | Edit
Use human-readable and SEO-friendly permalinks for Participants Database records

Version 1.7 | By xn*au webdesign | Visit plugin site | Support | Check for updates
Select Participants Database reCAPTCHA
Participants Database reCAPTCHA
Deactivate | Edit
add reCAPTCHA validation

Version 1.2 | By xn*au webdesign | Visit plugin site | Support | Check for updates
Select PDB HTML Form Element
PDB HTML Form Element
Deactivate | Edit
a general-purpose form element that simply displays HTML

Select Quick and Easy FAQs
Quick and Easy FAQs
Deactivate | Edit | Settings
A quick and easy way to add FAQs to your site.

Version 1.1.0 | By Inspiry Themes | View details
Select Shortcode Menu
Shortcode Menu
Deactivate | Edit
To display menu’s everywhere like sidebar, header, footer, pages, posts or theme template with effective styling and customization using shortcode.

Version 3.2 | By Amit Sukapure | View details
Select Simple Custom Post Order
Simple Custom Post Order
Deactivate | Edit
Order Items (Posts, Pages, and Custom Post Types) using a Drag and Drop Sortable JavaScript.

Version 2.3.2 | By Colorlib | View details
Select Simple Lightbox
Simple Lightbox
Settings | Reset | Deactivate | Edit
The highly customizable lightbox for WordPress

Version 2.6.0 | By Archetyped | View details | Feedback & Support
Select Simple Twitter Tweets
Simple Twitter Tweets
Deactivate | Edit
Display last x number tweets from Twitter API stream, store locally in database to present past tweets when failure to access Twitters restrictive API occurs

Version 4.4 | By Ashley Sheinwald | View details
Select Slimstat Analytics
Slimstat Analytics
Deactivate | Edit
The leading web analytics plugin for WordPress

Version 4.7.3.1 | By Jason Crouse | View details
Select Subscribe2
Subscribe2
Deactivate | Edit
Notifies an email list when new entries are posted.

Version 10.22.1 | By Matthew Robinson, Tanay Lakhani | View details | Settings | Donate
Select To Top
To Top
Settings | Deactivate | Edit
To Top plugin allows the visitor as well as admin to easily scroll back to the top of the page, with fully customizable options and ability to use image.

Version 1.5.3 | By Catch Themes | View details
Select Vimeography
Vimeography
Settings | Deactivate | Edit
Vimeography is the easiest way to set up a custom Vimeo gallery on your site.

Version 1.5.3 | By Dave Kiss | View details
Select WP Advanced PDF
WP Advanced PDF
Settings | Deactivate | Edit
WP Advanced PDF plugin is a pdf generator for wordpress posts to pdf to archive and/or printing. Blog readers can export post into pdf and can print or send it to registered email address.

Version 1.1.5 | By CedCommerce | View details | Demo | Documentation
Select WP Mail SMTP
WP Mail SMTP

P.S. I’ve tried deactivating all other plugins and it makes no difference.

First, try switching theme to the default one (twentyseventeen) and deactivating all the plugins by xn*au webdesign.

That made no difference.

I have many forms on the site. If this can’t be resolved I’ll have to look for an alternative form plugin ??
Do you think you can help?

In your first comment:

Validation errors:

Additional headers: Reply-To: [your-email]
To: [your-email]

What did you mean by this? Do you have any configuration errors in the admin page?

These are the errors it shows – why are they suddenly errors – with no changes having been made and the form worked perfectly well prior to this?

I don’t understand. I see no error in it. Where did you find it? I guess it’s in the Mail tab settings, no? Can you upload a screenshot of it?

Exactly! Yet your plugin shoes errors when they’re not. Same on all my forms. I have screenshots. How do I upload images here?

https://tvtwins.uk/mango/wp-content/uploads/Capture.JPG
https://tvtwins.uk/mango/wp-content/uploads/20171115_074759.png
https://tvtwins.uk/mango/wp-content/uploads/20171115_074827.png

Can you please delete this thread – or at least my links?
Resolved by uninstalling and reinstalling plugin