Like so many, my older Roku 3 started telling me I needed to add a MicroSD card. After finding a recommendation from Roku online that the Roku 3 (4200x) should have a 4GB MicroSD card, I ordered just that... Sandisk 4GB Class 4. With no luck getting it to work on my own, I found this thread and tried every suggestion. I can't tell you how many times I ejected/reseated the card trying to get it to be accepted. I formatted it, I long formatted it, no joy. I finally gave up and grabbed another 8GB Class 10 card I had for a Game Camera, it too was a Sandisk. Again, formatted, long formatted, ejected, reseated, no joy. Honestly, I don't remember if it was earlier in this thread or on another but someone linked a Kingston 4GB Class 4 MicroSD on Amazon that they said worked for them. So I ordered one. It showed up today and right out of the package and into the MicroSD slot on the Roku 3, I got the screen notification that a MicroSD card had been discovered, would I like to format it? I did and all is well. Automatically a few of the rotational apps were downloaded and installed and even at just 4GB, only about 7% is being used.