Failed to solve a imprecise hardfault error

i m working on lpc1788.
I use Keil rtos and mailbox to pass the data from the uart handler (as read from a thread on this forum).
All was working well till date, untill i added a few bytes of code on saturday.
The seventh string that is received to the uart creates an imprecise error. it always has to be the 7th (irrespective of the size of the previous strings)

to check the cause, i came across this piece of code, but doesnt work in keil

__attribute__((naked))
void HardFault_handlerAsm(void)
{
        __ASM (         ".syntax unified\n"
                                        "MOVS      R0, #4  \n"
                                        "MOV       R1, LR  \n"
                                        "TST       R0, R1  \n"
                                        "BEQ       _MSP    \n"
                                        "MRS       R0, PSP \n"
                                        "B         HardFault_HandlerC      \n"
                                "_MSP:     \n"
                                        "MRS       R0, MSP \n"
                                        "B         HardFault_HandlerC      \n"
                                ".syntax divided\n"
                        ) ;
}



void HardFault_HandlerC(unsigned long *hardfault_args){
        volatile unsigned long stacked_r0 ;
        volatile unsigned long stacked_r1 ;
        volatile unsigned long stacked_r2 ;
        volatile unsigned long stacked_r3 ;
        volatile unsigned long stacked_r12 ;
        volatile unsigned long stacked_lr ;
        volatile unsigned long stacked_pc ;
        volatile unsigned long stacked_psr ;
        volatile unsigned long _CFSR ;
        volatile unsigned long _HFSR ;
        volatile unsigned long _DFSR ;
        volatile unsigned long _AFSR ;
        volatile unsigned long _BFAR ;
        volatile unsigned long _MMAR ;

        stacked_r0 = ((unsigned long)hardfault_args[0]) ;
        stacked_r1 = ((unsigned long)hardfault_args[1]) ;
        stacked_r2 = ((unsigned long)hardfault_args[2]) ;
        stacked_r3 = ((unsigned long)hardfault_args[3]) ;
        stacked_r12 = ((unsigned long)hardfault_args[4]) ;
        stacked_lr = ((unsigned long)hardfault_args[5]) ;
        stacked_pc = ((unsigned long)hardfault_args[6]) ;
        stacked_psr = ((unsigned long)hardfault_args[7]) ;

        // Configurable Fault Status Register
        // Consists of MMSR, BFSR and UFSR
        _CFSR = (*((volatile unsigned long *)(0xE000ED28))) ;

        // Hard Fault Status Register
        _HFSR = (*((volatile unsigned long *)(0xE000ED2C))) ;

        // Debug Fault Status Register
        _DFSR = (*((volatile unsigned long *)(0xE000ED30))) ;

        // Auxiliary Fault Status Register
        _AFSR = (*((volatile unsigned long *)(0xE000ED3C))) ;

        // Read the Fault Address Registers. These may not contain valid values.
        // Check BFARVALID/MMARVALID to see if they are valid values
        // MemManage Fault Address Register
        _MMAR = (*((volatile unsigned long *)(0xE000ED34))) ;
        // Bus Fault Address Register
        _BFAR = (*((volatile unsigned long *)(0xE000ED38))) ;

        __asm("BKPT #0\n") ; // Break into the debugger

}