Roku Media Player Does Not Recognize USB Flash Drive

I got it! 

My situation: I had a USB stick for media. I took it out to add more media to it. I put it back. When I opened the app, I got the no-recognize error.

In my case, it was somehow a permission issue. The device forgot it was allowed to access the stick.

Solution: Take the USB stick out. Go to the Roku Media Player app. Put the USB stick in. That'll bring up the ALLOW? prompt. Allow it to access the stick. Once it is allowed to access it, it recognizes it. 

Hope this works for you!