As the app itself says "Roku software update 7.1.0 4062-06 has broken TV Cast on some Roku devices. We are preparing an app update. Please stay tuned." I can confirm that this application has stopped working with my Roku 2, after months of functioning fine. Heres hoping the promised update appears soon.
UPDTE: Roku has released software version 7.2.0 4100-06, but TV Cast still doesnt work. Video streaming in the official Roku app also remains broken.
Ed The iPad Fan about TV Cast for Roku App, v1.8