If I understand correctly. You can see the on board debug probe, but this reports an error when trying to connect to the MCU...
The first thing I would check is the setting of the Link JP1. This controls whether the on board debug probe connects to the LPC4367, or whether it is used to control an external board. The jumper should connect the left and mod pins of this 3 pin header.
SWD VREF power selection – 3 position jumper pins. Jumper 1 – 2 (default) when on-board Target MCU is connected to either the on-board Link2 debug probe or an external debug probe.
Jumper 2 – 3 when on-board Link2 debug probe is used to debug an off-board Target MCU.
Yours,
LPCXpresso IDE Support