I tryed again the installation but it failed again

same step : reboot after 30s during obuntu installation. This time, i use the "unlocker" of seaniko. But when i flash it, my device reboot. Is it possible de check that this unlocker installation is right ? And a last question, after the use of MFG tool, is it necessary to flash again the unlocker?
I don't understand why my installation failed. The only difference with the other users is that i have installed the last firmware of Boxtor... (my M92 comes from e reader shop)
Thanks in advance !