Hi,
I finally found someone that has my same problem. My mbed NXP LPC1768 halted in Chip_ENET_Init() function, but it didn't always halt in pENET->MAC.MAC1 = ENET_MAC1_PARF line, but could also stop inside the resetENET(pENET) call in a indeterministic way.
The debug error showed is the following:

and than, if I try to rerun the project a “Cannot halt processor” console error appears and after this error I become no longer able to test any project on the LPC1768 with MCUXpresso, because if I try to run any project, the error always return.
The only way to recover the LPC platform is to use MBED Studio to build a .bin execution file, and load it in the device driver of LPC1768. After power-cycle the board by disconnecting and reconnecting the cable, I can still use MCUXpresso to run projects.
Moreover I found that the 0x50000000 address, showed in the debug console error, is the ethernet peripherals base address. Why should an access on the ethernet peripherals base address give this error?
Trying to eliminate the preprocessor declaration __USE_LPCOPEN as suggested by Alexis nothing changed, the problem remains and the behavior is the same.

What can I do to solve this problem? Every demo project with an ethernet communication stop with this error on Chip_ENET_Init() function, while a freertos demo project without an ethernet communication works well (for example the freertos_blinky project). I think that the problem is on the ethernet peripherals base address. Could it be?