admin-ajax error

Hey! I know there are probably tons of topics with this questions .. but I couldn’t find any so I had to ask.
Well.. i’ve got a problem.Everytime i try to delete something it says:
Forbidden
You don’t have permission to access /wordpress/wp-admin/admin-ajax.php on this server.
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ultimate-omarion.com
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This thing also appears when i try to add users , categories etc..
Please help!
Edit : sorry i’ve posted it in the wrong category.