Translation plugin

I have installed the WPML plugin to translate the website in two languages. With the main language (Spanish) there are no problems but with the other one (English) it does not allow me to save the changes in templates or footer in the Editor. I need to modify the templates in the English version so that they are the same as Spanish. The error is “The response is not a valid JSON response”. What can be the cause? How can we solve it? Thank you.