Try with sudo - that helped me.
[andranik@ubuntu:tmp ]$ ./uuu -b sd_all imx-boot-imx8mmevk-sd.bin-flash_evk fsl-image-validation-imx-imx8mmevk.sdcard
uuu (Universal Update Utility) for nxp imx chips -- libuuu_1.2.91-0-g3799f4d
Success 0 Failure 1
2:16 1/ 0 [Failure open usb device,Try ]
[andranik@ubuntu:tmp ]$ sudo ./uuu -b sd_all imx-boot-imx8mmevk-sd.bin-flash_evk fsl-image-validation-imx-imx8mmevk.sdcard
[sudo] password for andranik:
uuu (Universal Update Utility) for nxp imx chips -- libuuu_1.2.91-0-g3799f4d
Success 1 Failure 0
2:16 6/ 6 [Done ] FB: done