now, all my hosting configuration was revised, memory_limit is 128mb, has was suggested, and the problem occures when i change menu item layout to "isotope" as defined in JA Mono documentation for "Projects" page/
I i change layout to "Category blog" layout, menu item works fine without any 503 or 404 error. you have my full permission to make any changes and checks as you need to solve the problem/
Thanks