Maybe trying to downgrade firmware rather than going up? - try the latest firmware available.
Or reactivation lock was on?
There are a few PIT files around which should sort you out once you have it.
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// LG G3 (D855) // Stock // Stock //
// HTC One (M8) // GPE Stock // Stock GPE//
// Nexus 7 (flo) // Android L // Stock//
S3(White) > M7(Red) > Note 3(Black) > Nexus 5(Black) > M8(Gunmetal)/LG G3 (Titan Grey)