Just wanted to follow up on my Roku not recognizing my SD card...
Over and over Roku kept insisting it was my fault, I didn't insert the card correctly, etc., etc.
Then one day my Roku announced it had a major upgrade, which took quite a while and ended up putting itself into an endless loop of a video showing me all the cool new features, most of which I didn't want. I had to unplug the box to get it to stop and reset.
And guess what? That SD card that nobody could explain why wasn't recognized... now was recognized. My my.
I have popped out the unrecognized micro while my Roku2 was powered, but with HDMI removed. It recognized my 64 GB micro and is now formatting.
Try Roku2 powered on. Then add MicroSD card. That worked for me.
This was my experience too.