SCL3711: IOError no response from pn53x

I'm tryng to build a simple P2P data exchange between a Samsung Nexus (ICS 4.0.3) and SCM SCL3711 and now i'm trying to send data from the reader to the smarthphone.
I have already modified the script snep-test-client, following the answer to the question https://answers.launchpad.net/nfcpy/+question/184591, but I can't understand why few times everything is working properly and sometimes the script generates the following error:

$ python terminal.py -d nfc.llcp -d nfc.snep

enable debug output for module 'nfc.llcp'
enable debug output for module 'nfc.snep'
searching for a usable reader
searching for a usb bus reader
path match for 'usb' (or no path given)
trying usb:005:006
import nfc.dev.pn53x_usb
chipset is a PN533 version 2.7
using SCM Micro SCL3711-NFC&RW at usb:005:006
activated a p2p target in 424 kbps active mode
llc cfg {'recv-lto': 1500, 'send-miu': 128, 'send-agf': True, 'send-lto': 1500, 'send-lsc': 3, 'recv-miu': 1024, 'send-wks': 1, 'rcvd-ver': (1, 0)}
LLCP Link established, I'm the DEP Initiator
Local LLCP Settings
  LLCP Version: 1.1
  Link Timeout: 1500 ms
  Max Inf Unit: 1024 octet
  Service List: 0000000000000011
Remote LLCP Settings
  LLCP Version: 1.0
  Link Timeout: 1500 ms
  Max Inf Unit: 128 octet
  Service List: 0000000000000001
SEND 0 -> 0 SYMM
I'm the Initiator
   connect to urn:nfc:sn:snep
in exchange => IOError no response from pn53x
shutdown on link disruption
closing service access point 32
shutdown socket DLC 32 <-> None CONNECT RW(R)=None V(S)=0 V(SA)=0 RW(L)=1 V(R)=0 V(RA)=0
DLC (None,None) CONNECT close()
closing service access point 1
shutdown requested
closing service access point 0
llc run thread terminated
Traceback (most recent call last):
  File "terminal.py", line 155, in <module>
    main()
  File "terminal.py", line 66, in main
    snep.connect("urn:nfc:sn:snep")
  File "/home/m0m0z/PyDev-Workspace/NFC-Terminal/nfc/snep/client.py", line 71, in connect
    nfc.llcp.connect(self.socket, service_name)
  File "/home/m0m0z/PyDev-Workspace/NFC-Terminal/nfc/llcp/__init__.py", line 136, in connect
    return _llc.connect(sid, dest)
  File "/home/m0m0z/PyDev-Workspace/NFC-Terminal/nfc/llcp/llc.py", line 500, in connect
    socket.connect(dest)
  File "/home/m0m0z/PyDev-Workspace/NFC-Terminal/nfc/llcp/tco.py", line 423, in connect
    pdu = super(DataLinkConnection, self).recv()
  File "/home/m0m0z/PyDev-Workspace/NFC-Terminal/nfc/llcp/tco.py", line 123, in recv
    return self.recv_queue.popleft()
IndexError: pop from an empty deque

I thought about a timeout error related to the device or any related library, but I have not found any solution to this behavior.

Thanks for the help