Issue: exception in call user callback func of ROJS.lpConnectionLibrary: TypeError: chat.__stopChatComm is not a function

Hi. I use javascript chat.
When I try use OnStop event:

var lpChatConfig = {
    apiKey : '<MyKey>',
    jsApiSrcDomain : 'dev.liveperson.net',
    lpNumber : '<MyNumber>',
    onLoad : function() {
        window.lpc= new lpChat();
    },
    onLine : myOnLine,
    onError : myOnError,
    onAvailability: myOnAvailability,
    onStop : myOnStop

And I click "Stop Chat" button on operator console. I see in browser window next error:

"exception in call user callback func of ROJS.lpConnectionLibrary: TypeError: chat.__stopChatComm is not a function"

I have a myOnStop function in file:

function myOnStop( reasonId, reasonText ) {
  if(reasonId == 1) {
     //alert('Agent stopped chat');
  }
  if(reasonId == 2) {
     //alert('Agent disconnected');
  }
  if(reasonId == 4) {
     //alert('Visitor stopped chat');
  }
  if(reasonId == 5) {
     //alert('Visitor disconnected');
  }
  if(reasonId == 7) {
     //alert('Visitor disconnected for other reasons');
  }
  if(reasonId == 8) {
     //alert('Visitor was no longer in chat');
  }
  if(reasonId == 9) {
     //alert('Visitor logged out');
  }
  if(reasonId == 10) {
     //alert('Visitor closed the chat');
  }
  if(reasonId == 12) {
     //alert('Visitor abandoned the chat request');
  }
}

Could you help me?