Hi AndDiSa and thank You
Why would it give an error on system.img? What are you trying to flash? Can you paste the complete command you enter, including all the output fastboot gives?
C:\adb>fastboot.exe devices NNF6R18607002512 fastboot C:\adb>fastboot flash recovery_ramdisk TWRP-3.2.2-1-MediapadM5.img target reported max download size of 471859200 bytes sending 'recovery_ramdisk' (11280 KB)... OKAY [ 0.250s] writing 'recovery_ramdisk'... OKAY [ 0.108s] finished. total time: 0.359s C:\adb>fastboot reboot rebooting... finished. total time: 0.028s