More -- I think the message may be saying Magic bitmask 0x???? not found (not that there are actually question marks in the message, but the digits are going by too quickly to read).
Googling, it looks like many people have encountered this (one site even referred to it as the "infamous jffs2_scan_eraseblock(): Magic bitmask 0x1985 not found"), but I haven't come across any explanation of how to get past it....
