There seems to be some issue with the iPad communicating with the Roku. I would start with turning the power off and on again on your iPad and Roku. You may need to reset the Roku as well.
If neither of these suggestions helped, I would take a look at the bottom bullet in the Roku FAQ section. It has a few more suggestions to try.
Hope this helps!
Until recently I was able to stream to my TV using my Slingplayer 500. Tried yesterday and next to the Roku device ID there appears a triangle with an exclamation point. Have reloaded the Sling player app on the Roku and on the phone. Tried to manually connect. Nothing helps. I also get another message when I try to connect, "Slingplayer app is being installed on your Roku. If installation fails, on your TV, install the app from the Slingplayer channel store on your Roku. When installation is complete, press watch button to start watching on your TV." I don't see a Slingplayer channel store on the Roku.