How ot get big XML responce from web servicet (QTP, POST request)

I have next code:

 Set HTTP = CreateObject("MSXML2.XMLHTTP") 
    request="URL"
    HTTP.Open "POST", (request), False
    HTTP.setRequestHeader "Content-Type", "application/x-www-form-urlencoded"
    'HTTP.setRequestHeader "Content-Type", "text/xml"
    HTTP.send("recordName=some parameters")
    set response=HTTP.responseXML

The question is: When responce is not so big, Im able to get xml DOM object

set response=HTTP.responseXML

But if this response is bigger that some amount, the HTTP.responseXML object is empty. The same behaviour could be seen for GET request. Is there any other objects that could be used instead of XMLHTTP? Will really appreciate, if somebody could help with that.