IWDatasource failing to execute callback function

Matias

Hello,
I'm using an IWDatasource object in my form to call a datastore with dynamic parameters.
[html]
function handleBusinessUnitChange(item)
{
var selectedBU = item.getOptions()[item.getValue()].text;
var datasourceObj = new IWDatasource();
var dsParams = new IWMap();
var returnParams = new IWMap();
dsParams.put("Groups","WVR_Reviewers," + selectedBU);
datasourceObj.executeDatasource("setDatasourceValueCallback","LiveSite Groups Intersection",dsParams,returnParams);
return;
}

function setDatasourceValueCallback(resultObj, ctxParams)
{
alert("I'm back");
}
[/html]

the problem is that setDatasourceValueCallback is never called back, and I actually get a JS error in the console:

Sarissa.getDomDocument is not a function
iwexecuteDatasourceCallBack() dcapi_datasource.js (line 148)
var xmlDoc = Sarissa.getDomDocument();


I'm looking @ the call made by the DS, and the return seems to be correct:
[html]
setDatasourceValueCallback 426080=_iw_=test;C02889=_iw_=test2
[/html]

Has anybody encountered a similar issue using IWDatasource?