Cortex-A8 debug issues

Hi expert

Since I debug AM3354(Cortex-A8 Core)， I want to enable IRQ， so I write the assembler code:

IntrEnableIrq

    MRS     R0, CPSR             ; Pickup current CPSR
    BIC     R0, R0, #0X80        ; Clear interrupt lockout bits in CPSR
    MSR     CPSR_c, R0           ; Setup new CPSR value
    MOV     pc, lr               ; back 

and I put a break point in 

MSR CPSR_c,R0

and I run the program in full speed, then stop in MSR CPSR_c, then I run the program again,

but the program come to hard fault immediately.

I am sure the program run to error immediately, even not come to MOV pc, lr.

So I check the CPSR register's bits value, 

Bit7(IRQ set bit is cleared) .

It is really confused me a long time, ARM Mode is 10111(ABT mode), and I can change IRQ(bit 7)from 1 to 0, then the program 

come to error immediately , why this happen? I really need your help.

Best Regards

Jack