If the official recovery utility fails with a "Checksum Mismatch" or "File Format Error," you may need to rebuild the .fls file using Samsung’s low-level tool: or HxD (hex editor).
Samsung introduced a downgrade lock in firmware versions after V1.01.00.15 . You cannot directly flash older versions. To bypass: Fix Ml1660 V1.01.00.30.fls
: Drag the .fls file and drop it directly onto the usblist2.exe icon. A command prompt window will briefly appear showing the data transfer progress. If the official recovery utility fails with a