Problem with login

Hi, i have a serious problem with the login of my site ’cause when every user click on Login appears an error page like the links that i post in this topic.
My site is: http://lagattamangiona.it/coupon
The error page that appears when i click on login after write user and pass is this: http://www.lagattamangiona.it/coupon/coupon/Index.php

I think is a problem link to the url’s redirect of the button Login but i have no idea of where i have to change the code and what i have to write for no have bad results.

I also try to re-save permalinks unsuccessfully.

Can you help me? Please