Not to be narcissistic but after multiple failed attempts of trying to cast/mirror my device to my Roku via WiFi with help from the staff at Roku, i was able to fix this problem on my own. My first attempt of casting my device to Roku was a success, after that I could not. From my experience I noticed that ever time I linked my Android tablet to my Roku, my tablet stored the Roku connection information in an area called Remembered Groups. You need to clear this ever time you want to link your device after a disconnection. Go into your Settings/WLAN/Advanced (find this by looking for the 3 dots top right of screen, Lollipop version)/WLAN Direct and under Remembered groups you'll see your history of connections, in other words you'll find your Roku device that was previously connected. Prompt that, and it will ask you do you want to forget this group, click ok. Go back into your casting/mirroring screen in your settings and try to connect. This worked for me. I believe the problem lye with the stored information conflicting with my WiFi connection. I'm sure I could go into my router settings to fix this but to lazy. Let me know if this helps anyone.