problem in external interrupt handling in ARM LPC2138

hiiii

i am using ARM LPC2138 for my application.For one of my devices i am
using its external interrupt pin .i am compliling my code in ARM
mode.i am able to compile my code in KEIL as well as GCC without any
warning.i am printing some values in my ISR routine.

the problem is:
After executing the isr the system halts. Please suggest what could be
the problem.

i am initialising my external interrupt registers EXTMODE & EXTPOLAR
to 0x00
and interrupt vector registers as follows:

VICINTSELECT &= ~0x00004000;
VICINTCTRL14  = ( unsigned long
int )external_isr ;..................address of external isr routine
VICINTCTRL14  = 0x0000002E ;
VICINTENABLE |= 0x00004000;

in my isr i m printing some random values and resetting the flags and
interrupt vector address as follows:

EXTINT |= 0x01 ;
VICVECTADDR = 0x00000000; resetting the interrupt vector address to 0


Please suggest what could be the problem.
thank you