Confirmed, repartitioning fixed the problem:
$ sudo fdisk -l /dev/sdb
Disk /dev/sdb: 4063 MB, 4063232000 bytes 254 heads, 16 sectors/track, 1952 cylinders Units = cylinders of 4064 * 512 = 2080768 bytes Disk identifier: 0x0008e42c
Device Boot Start End Blocks Id System /dev/sdb1 * 1 1953 3967999+ c W95 FAT32 (LBA)
Now it boots.
Confirmed, repartitioning fixed the problem:
$ sudo fdisk -l /dev/sdb
Disk /dev/sdb: 4063 MB, 4063232000 bytes
254 heads, 16 sectors/track, 1952 cylinders
Units = cylinders of 4064 * 512 = 2080768 bytes
Disk identifier: 0x0008e42c
Device Boot Start End Blocks Id System
/dev/sdb1 * 1 1953 3967999+ c W95 FAT32 (LBA)
Now it boots.