error 65: access violation at C:0xFF00 : no 'execute/read' permission

Hello,I have a huge problem and I can't fix it for a days so I desided to ask you for help.My program is very simple but as you said before it's not imune for errors.I'm having this message: *** error 65: access violation at C:0xFF00 : no 'execute/read' permission.
And this is my code:

#include <REG2051.H>

#define SL P1_4
#define SR P1_5

#define A P1_6
#define EN P1_7

unsigned char F = 0x00;
unsigned char PF = 0;

void Go_To_Sleep (void)
{ PCON = 0x01;
}

void main (void)
{ IT0 = 0; EX0 = 1; EA = 1; Go_To_Sleep ();
} void Ext_Int (void) interrupt 0

{
F=~F;
if(F==0x00) { A=0; }
else { A=1; } while(PF==0) { EN=1; if(A==0) { if(SR==1) { PF=1; } } else { if(SL==1) { PF=1; } } } EN=0; PF=0;
} Thank you!