Dear friends,
I'm writing you to let you know how I have solved the problem at least for now. I had this problem three times and thought the problem might result from usb flash disk. I downloaded an mp3 analyzer software. I formatted my usb drive and did a search ".*" in my music folder. I have found many various filetypes like .bak .jpg .bat etc. Also most of the files i downloaded from internet was corrupted or interrupted in the middle. Analyzer software notified me and I deleted all of the problematic files. And what happened? Nothing happened for 5 months hopefully it won't happen again... Also I upgraded to the latest firmware but it was not about that because I have recently updated.