Hi Dani,
Yes it is a PHP page. The one I tried to edit was created with UE4.
But, once the problem strikes - even if I go to create a brand new page and apply a Universal Email behavior, then I edit in Dreamweaver (to edit the email that is sent), then go to save and continue working in the dialog box; that's when I get the error and I have to Force Quit Dreamweaver as it becomes completely unresponsive.
Best regards,
Brian