Since you will not tell me, I assume you are using a Philips LPC variant.
If that is the case, then when you configure a port pin in quasi-biadirectional mode which your definition does, you must write a "1" to that bit in the port register (p1) to allow input (interrupt). This is what the above has been about and if you had revealed that you were using a "non-standard" derivative, we would have been here long before.

Erik