I download and activate no-ip, i change server addr to my host name, but when i log-in, appear an error "Cannot Resolve Hostname"

How i fix it?

Your serveraddr must be 127.0.0.1

 

Your InternalIPHostname must be also 127.0.0.1 ( in both config files ) and your ExternalIP with your no-ip address.

Maybe he can try to set InternalHostname to 192.168.x.x depending on his router, otherwise he might not be able to log in.