I write this with Keil 7.01 .

I got " error C253 internal(undefine label)" message.
//----------------------------------------
#include <reg51F.h>

unsigned char a,b ;

void main(void)
{
while(1) {} //<--- *** if erase this line it's ok
while(1)
{
switch(a)
{
case 0x0b: b=a ; break ;
case 0x02: b=a ; break ;
case 0x03: b='0' ; break ;
case 0x04: b='0' ; break ;
case 0x05: b='0' ; break ;
case 0x06: b='0' ; break ;
case 0x07: b='0' ; break ;
case 0x08: b='0' ; break ;
case 0x09: b='0'; ; break ;
case 0x0a: b='0' ; break ;
case 0x1c: b='0' ; break ;
}
}
}

If I erase the while(1){} line everything is ok. but I want to keep it for some testing purpose such as blinking LED.
So. anyone know what's happen to this code
Thanks