When the LPC17XX/LPC24XX gets into a bad state, you need to short the ISP entry signal to ground while programming.
Contact us for the revision 4 schematic for the SOMDIMM module.
On J1 you need to short pins 3 and 4 together, then use the JLink to reprogram the unit.
If you purchased a USB-ISP then you should have a cable that will plug into the SOMDIMM’s J1, if not you can use a small flat head screw driver stuck in the middle of the pins to short them together