The wrong router password/username is a symptom that the Setup Assistant; isn't able to connect through your router via Universal Plug and Play; (uPnP). It doesn't actually mean specifically that you provided the; wrong credentials. If you're router has uPnP options, its probably disabled or using an conflicting version for the Slingplayer. You can try enabling uPnP within its menu or finding a firmware upgrade to update; the router.
Another way is to bypass the process, by opting for the "If you're an advance user and would like to configure your router manually" part of the "Setup Internet Viewing" portion of "Setup Assistant". There you'll see an checkbox for "My router is not listed"; check mark and click next and you'll get a screen summarizing your; Slingbox's information.; This is the information you'll need to create; the necessary port forwarding rules on you router.
If you still need step by step instructions on how to create port forwarding rules, then check this webpage (http://portforward.com/english/applications/port_forwarding/SlingBox/SlingBoxindex.htm) and you should find one that represents your router. Once you've; created the port forwarding rule, then go back to the setup assistant; and continue stepping through it to test if your rules are working.