406 Not Acceptable

Hi. I use 2.5 wordpress.
I have a problem. When i try to edit a “page” i receive page with this error : “406 Not Acceptable
An appropriate representation of the requested resource /wp-admin/page.php could not be found on this server.”

page.php is there. I never make changes in that file.

P.S. when i try to make a new page i receive same error.

P.S. I see that i receive same this error when i try to make Custom structure :
“………/wp-admin/options-permalink.php could not be found on this server……..”