Facebook SDK 7.8 Invalid Hash key

I have a problem with facebook sdk, the very first time I tried to login it actually worked with the key hash I got from Unity, the second try and thereafter i cant login anymore.
It says “Invalid key hash. The key hash ******** does not match any stored key hashes. Configure your app key hashes

when i build app in debug mode it works fine but in release mode it gives this kind of problem . im confused how to solve this problem.

Did you set the Key Hash as Facebook SDK document ?
make sure you add the right Key Hash to your Facebook App
the Key in Facebook config view is Debug Hash Key
you need to add Release Hash Key for release app

you could check this link for similiar issue
http://stackoverflow.com/questions/23674131/android-facebook-integration-invalid-key-hash

its so easy write your hash key like this in facebook site with capital and small letters and will work