Thank you very much ddabcd for sharing your expirience and ideas , that together find some solution , specially with help of guru kunix ! I hope kunix will can prepare for me modified firmware for 765 nuvi, from thread with 765 firmwares posted by our dear catymag ...

I think, cause kunix suggested in this post bellow for recovering Kenwood Garmin built-in gps navigation, that 0x66 region can cause that famous message "device is unable to program requested memory region""

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it seems that helped to lucky guy with that device , but same thing didn't help my 765 , even i removed that 0x66 region...

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It seems, problem on my nuvi 765 is more like one you described, with 0x48 problematic region...

p.s.
i found this about pk_files66.zip from nuvi's firmware,
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