In the action button - use absolute URL rather then relative URL
Also, will recommend you setting the base_url in config.php ...
Codeigniter is based on MVC itself - you dont need to use set_crud_url_path .. it automatically picks up the path and stuff..
that feature is required to be brought in use only when you have made some extra changes in the routes table
say for example ... you have controller file (Manage.php)
and in there you have function users...
now by default you will refer to the same as http://localhost/appname/manage/users
If you want to use it in other way - like http://localhost/appname/users ...
u need to set this in routing and the same then u need to use the function set_crud_url_path ...
It will be effective and in use only at that point of time.
Happy GCing :)