Restore configuration of switch

Restore configuration of switch

Hello and sorry for my english,

I have NCM since 1 month and i really don't unbderstand how to restore config on switch.

I have only cisco switchs. these switchs are added in NCM with "SSH-FTP" credential, this works, backup works.

But now i want to restore backup. So on switch, i use "upload config", i select the config i want, and i click on "upload"

I the NCM, i can see output for the switch : 
copy nvram:/startup-config tftp
%% Non-volatile configuration memory invalid or not present 

I don't understand. How it works ? what i have to do ?

thanks