My NSXMLParsing não está funcionando por causa do caractere "&" .. meu código está abaixo .qualquer ajuda, por favor?

 NSString *myRequestString = [NSString stringWithFormat:@"http://abc.com/def/webservices/aa.php?family_id=%d",self.passFamilyId];
//NSLog(@"Requested Service = %@",myRequestString);
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:[NSURL URLWithString:myRequestString]];
[request setHTTPMethod: @"POST" ];
NSData *downloadedData = [ NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];

NSString *str = [[NSString alloc] initWithData:downloadedData encoding:NSASCIIStringEncoding];
//NSString *contentString = [str stringByReplacingOccurrencesOfString:@"&" withString:@"&"];
NSData * data=[str dataUsingEncoding:NSUTF8StringEncoding];


//NSLog (@"string is :%@" ,str);    

NSXMLParser *xmlParser = [[NSXMLParser alloc] initWithData:data];   

// Call the XMLParsers's initXMLParse method.
ClientDetailXmlParser *parser = (ClientDetailXmlParser*)[[ClientDetailXmlParser alloc] initXMLParser];
[xmlParser setDelegate:parser];
BOOL success = [xmlParser parse];

// Check for XML parsing.
if(success) 
{
    NSLog(@"No Errors in clientDetailXml.xml");     
}
else 
{
    NSLog(@"Error Error Error in clientDetailXml.xml!!!");
}   

[parser release];
parser = nil;

if (objClientAddUpdate != nil) {
    [objClientAddUpdate createBubbleList];
}