Lpc2000

On a project I'm working on I have several interrupt service routines.
 All of them work fine except for one of them that is on the external
interrupt 0.  The ISR will be sucessfully called once and the system
hangs upon exiting the ISR.  I have defined a default ISR to see if
spurious interrupts were a problem, and the default ISR never gets
called, so all seems well there.  Any sugestions as to what might be
the problem?

Thanks, 
Reggie McMurtrey