No I2C interrupt with LPC2387

I know I must be making a simple error, but it's eluding me. I had the I2C working fine on the MCB2300, but now I've moved it to my own board which is very similar to the MCB as far as the I2C is concerned. The problem appears to be that the interrupt service routine is never getting called. I have gone through all of the documentation, verified that the interrupt enables are set, the VIC is set up, etc. I'm even using the basic code from the examples, but when it goes to start the I2C master transfer the STA bit is set, then it times out never going to the interrupt routine. I have verified by polling that the SI bit is getting set as expected. Can anyone point to where I might be going wrong? Can provide code but as I said it's basically the same code as the example.