ok then ,end the onsubmit bracket to the last instead of the glideajax call .

also change the getXML and its function try:

for(var j=0;j<arr.length;j++){

var ga=new GlideAjax('siteDetails');
ga.addParam('sysparm_name','sitecheck');
ga.addParam('sysparam_id',arr[j].toString());

var answer=ga.getAnswer();
if(answer=='false')
{
g_form.clearValue('name1');
alert("error");
return false;
}//if ends

}//for ends

}//onsubmit