As you have an older Slingbox, the password that the unit is asking for is likely the Administrator Password. This would have been created when you first set up the Slingbox and may not have been used since. Luckily, you should be able to change this password from any location using the steps in the following article:
If this does not work, you will need to reset the Slingbox at the home location and set this back up. I'll link the reset and reconfigure information below as well, just in case:
I hope this helps!
Sling Media Technical Support