I could finally sort it out by deleting the configuration and clicking on the debug button arrow and selecting Debug As > C/C++. But it wouldn't work just by starting a new debug configuration.
That doesn't work here, mate.
Not even re-installing LPCXpresso.
Neither moving project files (cleaned) to a fresh folder and changing workspace.
TG it's free... poor chaps who paid a penny...
Removing breakpoints didn't help as well, as pointed in another thread.
Well... finally... click on the Debug down arrow, then Debug As > 1 C/C++ (NXP...)
Or else in a whole year nobody else has tripped on this or users don't come here or there aren't so many users.