[j-nsp] M120 Boot Up Error

[Abhi]

Hi 

we have 2 M120 router each with 2 RE; all the 4 RE while booting initially are throwing the following messages.

mountroot>
panic: Root mount failed, startup aborted.
db_log_stack_trace_cmd(c0d196c0) at 0
panic(c0c62be0,c7734ca8,c0514dba,0,f3cd8d10) at 0
vfs_mountroot(c7734ca8,c7735600,debdfb38,3c620096,9714cfea) at 0
start_init(0,f3cd8d38) at 0
fork_exit(c0514dba,0,f3cd8d38) at 0
fork_trampoline() at 0
--- trap 0x1, eip = 0, esp = 0xf3cd8d6c, ebp = 0 ---
KDB: enter: panic
[thread pid 1 tid 100006 ]
Stopped at      kdb_enter+0x37: pushl   $-0x1
db>
db>reset

after i get this message i type in "reset" then the RE reboots and this time it boots from image from Hard Disk and gives message

JUNOS 8.5R1.13 built 2007-11-14 18:00:01 UTC
---
--- NOTICE: System is running on alternate media device  (/dev/ad2s1a).

on thing i have figured out is the image on flash has corrupted somehow for all the RE's.

How do i correct this situation?

Thanks in Advance

 Regards
Abhijeet.C