Thank you for posting your question to the Slingbox Community. Based on the information you've provided, it sounds as though your device is not currently set up to support streaming video outside of your home network. As far as what could have changed to cause this to happen suddenly... if you are viewing your Slingbox via a mobile or connected device, a software update could have occurred with the Slingplayer App that requires you to reconfigure your Slingbox at home to ensure it is setup properly to work with the new version of the player app. Without knowing the model of your Slingbox or the type of device you are using to connect remotely, it is impossible to know for sure.
The resolution might require you to port-forward you Slingbox (i.e. ensure that the correct ports are open on your home router). Here are some articles and resources that will assist you in successfully portforwarding your Slingbox
The second resource listed is a public website that provides portforwarding instructions for just about every router/modem manufactured. It is a wonderful resource the provides step by step instructions on how to open the ports of your router to any number of electronic devices (including Slingboxes). Keep in mind that portforwarding a router requires you to be at the home location with the Slingbox.
Hope this information was helpful!
Sling Media Technical Support