Perform the following commands and then check for the issue.
Under Config Mode:
Router(config)#Ip http server
Router(config)#Ip http secure-server
Router(config)#Ip http authentication local
Under Line vty 0 4:
Router(config-line)#login local
Router(config-line)#transport input telnet ssh.
After configuring Re-launch SDM with http/https authentication and try
clicking the "save" button by making some changes using SDM.
Also check for device memory available.