[Q] Help me pls

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http://forum.xda-developers.com – Hey guys I try to update my arc s lt18i but it cut down middle of the update I cant update anymore or I can repair than I try flashtool but it give an error like ( ERR_SEVERITY="MAJOR";ERR_CLASS="SECURITY_CLASS";ER R_STATIC="SIN_HEAD_VER";ERR_DYNAMIC="Failed to verify sin header"; ) and I didnt do unlock and my phone doesnt open.. Anyone have any solutions ? (HowTos)