I am having the same problem. I have been deactivating MailPoet for about a month every time I write a blog post so I can upload images to my post.
Otherwise I will get a upload error. Sometimes it actually uploads the image but no thumbnail. And other times it wont upload at all.
It’s very frustrating. I love the plugin. But it’s very inconvenient to have to go into maintenance mode deactivate Mailpoet, (So the javascript from my custom MailPoet email letter isn’t disabled making my front page look broken) just to write a post.
