Freescale K22 Cortex-M4  cpu : why Core Lock Up state occurs ???

I am using Cortex m4 processor from freescale K22,

In boot loader i download my firmware and after that I do following steps to soft restart

   // Disable - WatchDog and disbled IRQ.

  WDT_DISABLE();

  Disable_ALL_IRQ();

  DisableInterrupts;

  // Small delay is required before Soft RESET.

  delay1S();

  // SOFT RESET For K20

    SCB_AIRCR = SCB_AIRCR_VECTKEY(0x05FA) | SCB_AIRCR_SYSRESETREQ(1) ;

Now when MCU gets soft restart signal, next time it goes into CORE LOCK UP state

Ref:

ARM Information Center

Also after soft restart, i take jump to firmware with ODD address so as to ensure it is thumb mode.

my firmware address is 0X5000 + 1

Then it remains in Hard fault mode until i give power on reset then this hard fault state never occurs.

Can any body tell why this Hard fault state occurs when I soft restart??????

Thanks in advance!!!