When you're getting this error; the system isn't asking for your actual password in this situation. It is actually asking for your admin password, which you would have set up when you originally activated your Slingbox. I would try using "admin" first, but if this does not work, you would need to reset your Slingbox to factory settings. I have placed articles below going over the process, just in case:
- Slingbox.com - Forgotten the password on your Slingbox?
- Slingbox.com - How to reset your Slingbox to factory settings
- Slingbox.com - SlingPlayer repeatedly asks for the Administrator password
I hope this helps!!