Rfsa on "Move application in a new server but error in pages"

Hello to everyone.
I'm facing a problem with my website. I've recently move application in a new hosting without any changes or version updates.
It was that all run perfectly, but today I get an errore modifying an existing page. When I click on "update" or "preview", i get an error of page not found.
I made another test: if i modify a simple page with only text, updates are done perfectly and i can see updated page.
If i modify a more heavy page with image more test, i get this error.
If i work on post, i have no problem to add new post or update existing ones. The problem seems to be related to pages with many elements.
Can someone help me on this error? Is it a problem of php timeout setting or permission, or what? I have no idea.
thanks