All of sudden, when I access the "Add. Function" page in remote UI of iR5070, it asks for username and password.
I wonder if there is some defautl username / password that I can try?
There is no default user name/password.
If you are using ID numbers on the copier it just wants an ID number same as you use on the copier.
If you have a system manager user name/password set on the copier you need to use that.
If you can't remember system manager username/password you need to clear them in service mode PWD-CLEAR.