Debugging with mbed studio

Hi ,
I have just took out of the box or imported mbed-os_blinky_baremetal-5
into mbed stidion build it and trying to gebug it but here what
I got
0000913:INFO:board:Target type is stm32l151cc
0001079:INFO:dap:DP IDR = 0x2ba01477 (v1 rev2)
0001114:INFO:ap:AHB-AP#0 IDR = 0x24770011 (AHB-AP var1 rev2)
0001137:ERROR:ap:Transfer error while reading AHB-AP#0 ROM table: SWD/JTAG Transfer Fault @ 0xe00fffbc-0xe00fffff
Traceback (most recent call last):
File “c:\Users\dell\AppData\Local\Mbed Studio\mbed-studio-tools\python\lib\site-packages\pyocd\probe\”, line 315, in read_ap_repeat_callback

packages\pyocd\core\", line 299, in check_for_cores
raise exceptions.DebugError(“No cores were discovered!”)
pyocd.core.exceptions.DebugError: No cores were discovered!
“GDB server stopped unexpectedly with exit code 1”
How I can fix this error ? thanks