Why does /dev/mtd0 complain Intel TE28F160C3B as read only file system?

[Chen Yaoming]

# ls -l /dev/mtd0
crw-rw----    1 root     disk      90,   0 Oct 15  2001 /dev/mtd0

# ./mtd_debug info /dev/mtd0
mtd.type = MTD_NORFLASH
mtd.flags = MTD_CAP_NORFLASH
mtd.size = 2097152 (2M)
mtd.erasesize = 65536 (64K)
mtd.oobblock = 0
mtd.oobsize = 0
mtd.ecctype = MTD_ECC_NONE
regions = 2

region[0].offset = 0x00000000
region[0].erasesize = 8192 (8K)
region[0].numblocks = 8
region[0].regionindex = 0
region[1].offset = 0x00010000
region[1].erasesize = 65536 (64K)
region[1].numblocks = 31

# ./mtd_debug write /dev/mtd0 0x100000 16 /boot/vmlinuz
Copied 16 bytes from /boot/vmlinuz to address 0x00000000 in flash

# dd if=/boot/vmlinuz of=/dev/mtd0 bs=1k seek=1024
dd: writing `/dev/mtd0': Read-only file system
1+0 records in
0+0 records out

# ./mtd_debug erase /dev/mtd0 1048576 65536
MEMERASE: Read-only file system

# ./erase /dev/mtd0 0x100000 1
Erase Total 1 Units
Region 0 is at 0 of 8 sector and with sector size 2000
Region 1 is at 65536 of 31 sector and with sector size 10000
Performing Flash Erase of length 65536 at offset 0x100000
MTD Erase failure: Read-only file system