While testing Raspberry Pi3 i started Full Stress test for 30minutes and at the end i got error in the picture. Also when login over VNC and i try to open Dietpi OS SD card folder my File Manager windows freeze and later says not resposding. How to solve it? 
Hi,
IO errors indicate possible hardware failure (either PSU/SDcard/Board or all). Iād highly recommend a fresh image install, ideally using a different SDcard and PSU if available.
Also when login over VNC and i try to open Dietpi OS SD card folder my File Manager windows freeze and later says not resposding. How to solve it?
This will occur if you had a USB drive attached and at some point it was removed. The system will hang whilst it waits for the device to respond. More info here and how to resolve: Plex issues with mountingpoint - #2 by Fourdee