Checksum verification on install image failed on pix 515

after power shutdown and reboot from pix  515, the firewall cannot load the ios image anymore
6.3.(5) pix version


output :  Reading 1974784 bytes of image from flash.
################################################################################
#################################
imgsum_config: sumval(0xbd0d) md5(0x525ac23a 0x029b65fa 0x9b9c1ed3 0x6f7c4cad)
imgsum_verify: chksum(0x0   ) md5(0x75ef89e1 0x956d1be8 0xd803c5e0 0xb9022c77)
Checksum verification on uncompressed PIX image failed.


I tried to restore the image pix635.bin :


Using 1: i82559 @ PCI(bus:0 dev:14 irq:7 ), MAC: 0004.2746.c953
monitor> interface 1
0: i8255X @ PCI(bus:0 dev:13 irq:10)
1: i8255X @ PCI(bus:0 dev:14 irq:7 )
2: i8255X @ PCI(bus:0 dev:17 irq:9 )

Using 1: i82559 @ PCI(bus:0 dev:14 irq:7 ), MAC: 0004.2746.c953
monitor> address 192.168.1.4
address 192.168.1.4
monitor> server 192.168.1.2
server 192.168.1.2
monitor> file pix635.bin
file pix635.bin
monitor> tftp
tftp pix635.bin@192.168.1.2.....................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
................................................................................
....................................................
Received 2101248 bytes

Cisco Secure PIX Firewall admin loader (3.0) #0: Thu Aug  4 21:23:30 PDT 2005
Flash=i28F640J5 @ 0x300
BIOS Flash=AT29C257 @ 0xd8000
imgsum_config: sumval(0xfff7) md5(0x95976a4b 0x32251156 0x983b9a46 0x2770e99a)
imgsum_verify: chksum(0x0   ) md5(0xb7e7199e 0x94f909a9 0xc2e99293 0x7fe418be)
Checksum verification on install image failed.

additional info :


Cisco Secure PIX Firewall BIOS (4.0) #0: Thu Mar  2 22:59:20 PST 2000
Platform PIX-515
Flash=i28F640J5 @ 0x300