Issue with erase_all using JLink on nRF52

Question

I am using the JLink script to erase all the nRF52 DK. However, it does not seem to erase the flash. Can you please tell me if I am doing anything wrong?
I have cut-n-pasted the my procedure of erasing the device and then reading some locations to see if they are of 0xFFFFFFFF. 
 root@sw-14:/home//nordic/bake/projects/Release# make jlink_erase_all
Targets = [jlink_erase_all] PLATFORM = [PCA_10040]
make -s -f Makefile.project jlink_erase_all PLATFORM:=PCA_10040 BUILD_DIR:=_build
erase-all
SEGGER J-Link Commander V5.02g ('?' for help)
Compiled Oct 26 2015 19:00:10

Script file read successfully.
Info: Device "NRF52" selected.
DLL version V5.02g, compiled Oct 26 2015 19:00:05
Firmware: J-Link OB-SAM3U128-V2-NordicSemi compiled Jul 5 2016 08:42:09
Hardware: V1.00
S/N: 682227628
Emulator has Trace capability
VTarget = 3.300V
Info: Found SWD-DP with ID 0x2BA01477
Info: Found Cortex-M4 r0p1, Little endian.
Info: FPUnit: 6 code (BP) slots and 2 literal slots
Info: CoreSight components:
Info: ROMTbl 0 @ E00FF000
Info: ROMTbl 0 [0]: FFF0F000, CID: B105E00D, PID: 000BB00C SCS
Info: ROMTbl 0 [1]: FFF02000, CID: B105E00D, PID: 003BB002 DWT
Info: ROMTbl 0 [2]: FFF03000, CID: B105E00D, PID: 002BB003 FPB
Info: ROMTbl 0 [3]: FFF01000, CID: B105E00D, PID: 003BB001 ITM
Info: ROMTbl 0 [4]: FFF41000, CID: B105900D, PID: 000BB9A1 TPIU
Info: ROMTbl 0 [5]: FFF42000, CID: B105900D, PID: 000BB925 ETM
Cortex-M4 identified.
Target interface speed: 1000 kHz
Processing script file...

Writing 00000002 -> 4001E504

Writing 00000001 -> 4001E50C

Sleep(100)

Reset delay: 0 ms
Reset type NORMAL: Resets core & peripherals via SYSRESETREQ & VECTRESET bit.


Script processing completed.

root@sw-14:/home/nordic/bake/projects/Release# JLinkExe -device nrf52 -if swd -speed 1000
SEGGER J-Link Commander V5.02g ('?' for help)
Compiled Oct 26 2015 19:00:10
Info: Device "NRF52" selected.
DLL version V5.02g, compiled Oct 26 2015 19:00:05
Firmware: J-Link OB-SAM3U128-V2-NordicSemi compiled Jul 5 2016 08:42:09
Hardware: V1.00
S/N: 682227628
Emulator has Trace capability
VTarget = 3.300V
Info: Found SWD-DP with ID 0x2BA01477
Info: Found Cortex-M4 r0p1, Little endian.
Info: FPUnit: 6 code (BP) slots and 2 literal slots
Info: CoreSight components:
Info: ROMTbl 0 @ E00FF000
Info: ROMTbl 0 [0]: FFF0F000, CID: B105E00D, PID: 000BB00C SCS
Info: ROMTbl 0 [1]: FFF02000, CID: B105E00D, PID: 003BB002 DWT
Info: ROMTbl 0 [2]: FFF03000, CID: B105E00D, PID: 002BB003 FPB
Info: ROMTbl 0 [3]: FFF01000, CID: B105E00D, PID: 003BB001 ITM
Info: ROMTbl 0 [4]: FFF41000, CID: B105900D, PID: 000BB9A1 TPIU
Info: ROMTbl 0 [5]: FFF42000, CID: B105900D, PID: 000BB925 ETM
Cortex-M4 identified.
Target interface speed: 1000 kHz
J-Link>h
PC = 00076576, CycleCnt = CB78DC69
R0 = 00000001, R1 = 20007E22, R2 = 00000000, R3 = 00000000
R4 = 20003484, R5 = 20003B80, R6 = 20003B80, R7 = 00000001
R8 = 20002C88, R9 = 00000000, R10= 1FFF7F80, R11= 00000000
R12= 20007E08
SP(R13)= 20007F28, MSP= 20007F28, PSP= 00000000, R14(LR) = 00078BB5
XPSR = 61000000: APSR = nZCvq, EPSR = 01000000, IPSR = 000 (NoException)
CFBP = 00000000, CONTROL = 00, FAULTMASK = 00, BASEPRI = 00, PRIMASK = 00

FPS0 = 00000000, FPS1 = 00000000, FPS2 = 00000000, FPS3 = 00000000
FPS4 = 00000000, FPS5 = 00000000, FPS6 = 00000000, FPS7 = 00000000
FPS8 = 00000000, FPS9 = 00000000, FPS10= 00000000, FPS11= 00000000
FPS12= 00000000, FPS13= 00000000, FPS14= 00000000, FPS15= 00000000
FPS16= 00000000, FPS17= 00000000, FPS18= 00000000, FPS19= 00000000
FPS20= 00000000, FPS21= 00000000, FPS22= 00000000, FPS23= 00000000
FPS24= 00000000, FPS25= 00000000, FPS26= 00000000, FPS27= 00000000
FPS28= 00000000, FPS29= 00000000, FPS30= 00000000, FPS31= 00000000
FPSCR= 00000000
J-Link>mem32 0 2
00000000 = 20000400 000008E5
J-Link>mem32 1f000 2
0001F000 = 20010000 0002B2BD
J-Link>