You are passing two extra parameters to amx_kick, so you need another %s in your command..
Also, if you have spaces in one of the parameters (like the reason), then you should surround it in quotes, otherwise it will look like more than one parameter...
Code:
server_cmd("amx_kick %s %s", name, "^"You have been autokicked by the server.^"")
// or just do:
server_cmd("amx_kick %s ^"You have been autokicked by the server.^"", name)