help!!!

Can’t login to WP, Pages are being redirected with this message:

Warning: call_user_func_array() [function.call-user-func-array]: First argument is expected to be a valid callback, ‘eshop_cart_process’ was given in D:\Hosting\2523311\html\totalimage\main\wp-includes\plugin.php on line 395
WHAT DOES THIS MEAN????