Continuing execution after ISP in LPC81x series
I have the same problem. The ISP 'GO" command does not work for Cortex. In fact it can't work, because on a Cortex the initial SP is loaded from a particular address, not set by the code as for ARM chips.

My workaround is to reset the chip to force a reboot, by removing (and reapplying) the power. That's the only real way, because (at least on the chips I use) the 'reset' pin can be configured as GPIO.