LPC2132 : failed to copy arm to flash with IAP

I wanted to write a image to flash with IAP.
the function like this:

typeof IAPCALL (void)iaplocal(int *,int *);

IAPCALL iapcall=0x7ffffff1;

int cmd[5],ret[3];
cmd[0]=51;//cmd id
cmd[1]=0x1000;//flash start addr
cmd[2]=0x40002000;//ram start addr
cmd[3]=256;//size
cmd[4]=10000;//system clock

iapcall(cmd,ret);

i check ret,the ret[0] is 0,that means copy ram to flash success.(I use cmd 50 to prepare flash select before i call this fucntion and i also check the section of flash is blank).
but i compare the data in flash ,the flash is still blank.the data is not writen into flash.

I prefer your help! thanks!