In my experience, the SD card either works or it doesn't. Getting it in and out of the unit can be more difficult that it should be. The card should push all the way in and click. Likewise, taking it out, push in for a click and let it pop back out. It will only go in one way. Once in, and if it is recognized but the Roku, you should get a notification on screen to format and use the card. Bigger cards probably won't do you much good as I believe the Roku will only use so much and some cards are just not recognized. I have some Samsung cards that won't work but some no-name cheap brand works just fine.