404 Error when i click publish

Hi i need some help with this 404 error i am getting. I have moved the site from one server to another. the whole site works, its just when i update an existing page or when i try to add a new page, i get a 404 error.

Get this, when i switch themes, it works perfectly fine.

I have:
updated permalinks
updated htaccess manually
changed permissions
contacted the theme support and they were no help.

and no luck with any of it.

any help is appreciated, thank you.