Nested Interrupts

Hello everybody,
I'm using LPC2148 ARM7, programming with uVision3.

Now, I need nesting Interrupts. Following lines were used:

                AREA    NESTED_IRQ, CODE, READONLY
                ARM

                                EXPORT  nested_irq_enable
                                EXPORT  nested_irq_disable



nested_irq_enable                       ; Nested Interrupts Entry:

                                MRS             LR, SPSR
                                STMFD   SP!, {LR}
                                MSR             CPSR_c, #0x1F
                                STMFD   SP!, {LR}



nested_irq_disable                      ; Nested Interrupts Exit:

                                ldmfd   sp!, {lr}
                                msr             cpsr_c, #0x92
                                ldmfd   sp!, {lr}
                                msr             spsr_cxsf, lr


;/*****************************************************************************/

                END

Now, my Controller runs always in Prefetch Abort Handler. Does anybody know this problem?
Or does anybody see what I'm doing wrong?

Thanks for all Replys, Adrian