cosimo mercuro - 2010-01-13

When I attemp to connect from an internal webmin server to an internal router that has its own http server I receive this message:
"A username and password is required to login to 172.16.200.254, but none has been configured." and it is impossible to login to the router (I've no possibilities to put in the username and password because no authentication screen is displayed)
Where can I put username and password required?
Thanks in advance.
Ing. Cosimo MERCURO