An error occurred while sending the message, please try again.

If you see this error while trying to send the contact form:

The problem may be, that you are using new version of contact form, but your theme wasn't updated for that new module version. 

Edit this file in your theme: /themes/classic/modules/contactform/views/templates/widget/contactform.tpl

and change:

<footer class="form-footer text-sm-right"> <input class="btn btn-primary" type="submit" name="submitMessage" value="{l s='Send' d='Shop.Theme.Actions'}"> </footer>

to:

<footer class="form-footer text-sm-right"> <style> input[name=url] { display: none !important; } </style> <input type="text" name="url" value=""/> <input type="hidden" name="token" value="{$token}" /> <input class="btn btn-primary" type="submit" name="submitMessage" value="{l s='Send' d='Shop.Theme.Actions'}"> </footer>