is possibile to disassociate a quote from a quote product?

I have tried to do this:

var url = '/' + Xrm.Page.context.getOrgUniqueName() + "/XRMServices/2011/OrganizationData.svc/QuoteSet(guid'" + parentId + "')/";

   var option = "$links/quote_details(guid'" + childid + "')";

   var oData = url + option;

$.ajax({

       async: false,

       type: "POST",

       contentType: "application/json; charset=utf-8",

       datatype: "json",

       url: oData,

       beforeSend: function (xmlHttpRequest) {

           xmlHttpRequest.setRequestHeader("Accept", "application/json");

           xmlHttpRequest.setRequestHeader("X-HTTP-Method", "DELETE");

       },

       success: function (data, textStatus, r) {

           alert("success");

       },

       error: function (r, textStatus, errorThrown) {

           alert("Error: " + r.responseXML.text);

       }

   });

but I have this error

"Attribute: quoteid cannot be set to NULL"