Can't add new page to heading menu

Hello there, I'm using the catch food mania template for a client of mine and it will not allow me to upload a new page to the header menu. Every time I publish the site after making edits I receive the following message: Looks like something’s gone wrong. Wait a couple seconds, and then try again. Please help me remedy this situation as it's been weeks and I haven't been able to get anything done because of this error.