I think you need to add your web  part in safe  control.

Check out this link !

www.sharepointblogs.com/.../...art_deployment.aspx

but in which web.config file , we need to add tht safecontrol, i tried every web.config and i made snk file also , but its not working , it is giving the same error

A web  Part or Web Form control  on this Web part  Page cannot be displayed  or imported  because it is not registered  on this site  as safe.

You need to add in the web.config of your portal i.e. virtual server when you install the sharepoint. It is not web.config's which you find into web  extensions folder. Search for web.config on your server then you will get all the config files, select the one which is in your portal directory.

Don't forget...you will probably have to restart IIS after saving your changes, to make them take effect.