When trying to recover from a failed customer SW upgrade, an EX3400 switch gets a kernel panic.
- The methods using USB and TFTP show the same result.
- When trying to boot an snapshot created from another EX3400 switch , no access to USB image happens when booting. (can't load 'kernel').https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/ex-series-system-snapshot-boot-directory.html
Any suggestions? Unfortunately this device was purchased a year ago and customer didnt buy service. 
U-Boot 2016.01-rc1 (May 23 2016 - 08:45:58 -0700) VERSION=1.2.0
DRAM: AVS: 0x0
DEV ID = 0xdc14
SKU ID = 0xb547
DDR type: DDR3
MEMC 0 DDR speed = 750MHz
PHY revision version: 0x00044006
SF: Detected MX25L6405D with page size 256 Bytes, erase size 64 KiB, total 8 MiB
In: serial
Out: serial
Err: serial
FLASH bank: 1
Board: EX3400-48P
Net: bcmiproc_eth-0
Last Reset Reason: 8
Hit ^C to stop autoboot: 0
SF: Detected MX25L6405D with page size 256 Bytes, erase size 64 KiB, total 8 MiB
device 0 offset 0x3c0000, size 0x10000
SF: 65536 bytes @ 0x3c0000 Read: OK
## Checking Image at 61000000 ...
Legacy image found
Image Name: Juniper U-Boot Script File
Image Type: ARM Unknown OS Script (uncompressed)
Data Size: 1803 Bytes = 1.8 KiB
Load Address: 00000000
Entry Point: 00000000
Contents:
Image 0: 1795 Bytes = 1.8 KiB
Verifying Checksum ... OK
## Executing script at 61000000
Setting bus to 0
SF: Detected MX25L6405D with page size 256 Bytes, erase size 64 KiB, total 8 MiB
device 0 offset 0x140000, size 0x140000
SF: 1310720 bytes @ 0x140000 Read: OK
6113fffc: f1c1fb43 C...
crc32 for 61000000 ... 6113ffff ==> 43fbc1f1
Total of 1 word(s) were the same
starting USB...
USB0: phy ctrl 01d36440
Initial usb2h clock is: 000003fc
Initial usb2h clock is: 000003fd
iClk = 00000078, USBClk = 01536440
Bring usb2h_out of reset.......
usb2_reset_state is set and now it is: 00000000
usb2_reset_state is: 00000000
USB EHCI 1.00
scanning bus 0 for devices... 4 USB Device(s) found
scanning usb for storage devices... 2 Storage Device(s) found
SF: Detected MX25L6405D with page size 256 Bytes, erase size 64 KiB, total 8 MiB, mapped at 00000088
## Starting application at 0x00000074 ...
Consoles: U-Boot console
FreeBSD/armv6 U-Boot loader, Revision 1.2
(fbsd-builder@svl-bsdx-05.juniper.net, Wed May 18 12:32:06 PDT 2016)
DRAM: 2048MB
Number of U-Boot devices: 3
U-Boot env: loaderdev not set, will probe all devices.
Found U-Boot device: disk
Probing all disk devices...
Checking unit=0 slice=<auto> partition=<auto>... good.
/
can't load 'kernel'
Type '?' for a list of commands, 'help' for more detailed help.
lloader> install --format file:///junos-arm-32-15.1X53-D56.tgz
panic: free: guard1 fail @ 0x45c40 from /.amd/svl-engdata1vs1/occamdev/build/freebsd/head/20160518.183540_fbsd-builder_head.327854/src/lib/libstand/dosfs.c:248
--> Press a key on the console to reboot <--