title: S7-1200, Snap7: Exception: CLI : function refused by CPU (Unknown error)
body: <p>Running below snap7 client script for python using Siemens S7-1200 PLC shows the below common CLI refusal error. What is here the common problem and how to solve it?</p>
  
  <p>Script:</p>
  
  <pre><code>import snap7
  from snap7.util import *
  import struct
  import snap7.client
  from snap7.snap7types import S7AreaDB
  
  plc=snap7.client.Client()
  
  plc.connect('192.168.0.69',0,1)
  
  area   = 0x84
  start  = 0
  length = 1
  bit    = 0
  
  byte= plc.read_area(area,0,start,length)
  </code></pre>
  
  <p>Traceback error:</p>
  
  <blockquote>
    <p>No handlers could be found for logger "snap7.common"
    Traceback (most recent call last):
    File "", line 1, in
    File "/usr/local/lib/python2.7/dist-packages/snap7/client.py", line 242, in read_area
    check_error(result, context="client")
    File "/usr/local/lib/python2.7/dist-packages/snap7/common.py", line 69, in check_error
    raise Snap7Exception(error)
    snap7.snap7exceptions.Snap7Exception: CLI : function refused by CPU (Unknown error)</p>
  </blockquote>