Internal Server Error 500
 

I receive Internal Server Error ....
It returns Req.status = 500
Pl say the possibilities for this error,It would be helpful
Visual Studio 2003,Windows XP

configured basic Web Service and Application in same System

function CellClick(tableName,itemName, Btn)
{
var column =igtbl_getColumnById(itemName);
var oRow = igtbl_getRowById(itemName);
cnt = oRow.getCell(4).getValue();
StyleId = oRow.getCell(5).getValue();
if(column.Key=="Style")
{
cellobj = igtbl_getElementById(itemName);
cellobj.style.cursor = 'wait';
var x;
if(clickval==0) {
clickval=1;
window.status='Waiting for Page...';
LoadXmlForEncryption(CommonServiceUrl + '/common.asmx/GetEncryptString?InputString=' + StyleId);
}
}
}



function LoadXmlForEncryption(url)
{
// branch for native XMLHttpRequest object
//code for Mozilla, etc
if (window.XMLHttpRequest) {
req = new XMLHttpRequest();
req.onreadystatechange = GetEncryptString();
req.open("GET", url, true);
req.send(null);
// branch for IE/Windows ActiveX version
} else if (window.ActiveXObject) {
isIE = true;
req = new ActiveXObject("Microsoft.XMLHTTP")
if (req) {
req.onreadystatechange = GetEncryptString
req.open("GET", url, true)
req.send()
}
}
}


function GetEncryptString()
{
if (req.readyState == 4) {
if (req.status == 200) {
response = req.responseXML.documentElement;
EncStr = response.getElementsByTagName('OutputString')[0].firstChild.data;
LoadXmlForDocLock(CommonServiceUrl + '/common.asmx/LockEntry?sDocNo=' + StyleId + '&sPrefix=STY&sMisc=' + 'StyleEntry.aspx' + '&ToInsert=True');
} else {
alert("Problem in Web Service :\n" + req.statusText);
DefaultCursor();
}
}

}