i)Are you using the starter kit or CPU board evk, or custom board? Please also tell if this is the new board, or has it been programmed earlier and worked fine- but somehow stopped later- can you please give some details?
ii)On how many devices this problem occur? If it's on only one board, would be possible to test with another board?
iii) The VCCD is at 1.1 V and VDDD at 5V correct? Can you check voltage at Reset pin? And is the behaviour same at 3.3 V supply?