Cannot drop linked server login

Hi,

I tried to drop linked server login mentioned in linked server propeerties->security. When I clicked a login and selected delete, it process successfully. When I open again linked server properteis, this login is still there. I used both GUI and command line:
sp_droplinkedsrvlogin [ @rmtsrvname= ] 'rmtsrvname' ,
   [ @locallogin= ] 'locallogin'
GO

nothing works. There is no error. Any help.

Thanks