Problem of conflict with another module

Hi,
I am using Hikashop without any issues... until now.
I just installed a live chat for my website ( www.activehelper.com/ ) and since the installation Hikashop is not working.
when I am trying to use it I have the following lines of error:
Do you know how I can solve this problem?

My website is: www.theurgia.us
thank you.

______
Warning: simplexml_load_string() [function.simplexml-load-string]: Entity: line 2: parser error : Start tag expected, '<' not found in /home/content/....../html/theurgia/plugins/hikashopshipping/usps/usps.php on line 488

Warning: simplexml_load_string() [function.simplexml-load-string]: in /home/content/....../html/theurgia/plugins/hikashopshipping/usps/usps.php on line 488

Warning: simplexml_load_string() [function.simplexml-load-string]: ^ in /home/content/....../html/theurgia/plugins/hikashopshipping/usps/usps.php on line 488

Fatal error: Call to a member function xpath() on a non-object in /home/content/....../html/theurgia/plugins/hikashopshipping/usps/usps.php on line 321

What can I do... if I want to allow the sales with Hikashop?
Do you think this is an individual issue or global?

what you mean? I have to call USPS? install something else?...

OK I understand.

In fact this problem occurs when I click on "add to cart"...
Is there any relation with the thread you mentioned?

I cannot contact USPS today, so how I can solve the problem for today and allow the orders coming from my website?

Hi,

I applied the following modifications I found in the other thread in the the USPS plugin

_______________________

if ($isInternational)
$response_xml = $this->doUSPS($request, false);
else
$response_xml = $this->doUSPS($request, true);

if($response_xml === false) {
return;
}

_______________________

Now when I am trying to add a product to the cart I obtain the following message:

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator and inform them of the time the error occurred, and the actions you performed just before this error.

More information about this error may be available in the server error log.

_____________________________

Now there is not indication of the usps plugin problem...

What do you think?
I have to solve this issue as soon as I can.


Best,

Jean-Louis