Php Error

PHP Notice:  unserialize(): Error at offset 0 of 8 bytes in ...app/functions/fn.cart.php on line 2005, referer ...php?dispatch=orders.manage

After the upgrade to the 436 began to emerge this error. Where could be the problem?

It seems that the value of the $config['crypt_key'] variable in the config.local.php file of your installation was changed, that is why the issue occurs. Please replace it with the old one and check the issue again. Sensitive information is encoded with the help of this parameter.

I also have the same problem
I just restored my sql backup to new installation on new server.
can we find old cryptkey on sql backup?