I'm trying to send mail in iPhone using "SKPSMTPMessage" and I added the libraries,

In my class I added the following code:

- (IBAction)sendMail:(id)sender 
{
// if there are a connection
if ([theConnection isEqualToString:@"true"]) {
    if ([fromEmail.text isEqualToString:@""] || [toEmail.text isEqualToString:@""]) {
        UIAlertView *warning = [[UIAlertView alloc] initWithTitle:@"?????" message:@"?? ??? ????? ???? ????????" delegate:self cancelButtonTitle:@"?????" otherButtonTitles:nil, nil];
        [warning show];
    }else {

        SKPSMTPMessage *test_smtp_message = [[SKPSMTPMessage alloc] init];
        test_smtp_message.fromEmail = fromEmail.text;
        test_smtp_message.toEmail = toEmail.text;
        test_smtp_message.relayHost = @"smtp.gmail.com";
        test_smtp_message.requiresAuth = YES;
        test_smtp_message.login = @"[email protected]";
        test_smtp_message.pass =  @"myPass";
        test_smtp_message.wantsSecure = YES;

        NSString *subject= @"Suggest a book for you";
        test_smtp_message.subject = [NSString stringWithFormat:@"%@ < %@ > ",fromEmail.text, subject];
        test_smtp_message.delegate = self;

        NSMutableArray *parts_to_send = [NSMutableArray array];


        NSDictionary *plain_text_part = [NSDictionary dictionaryWithObjectsAndKeys:
                                         @"text/plain\r\n\tcharset=UTF-8;\r\n\tformat=flowed", kSKPSMTPPartContentTypeKey,
                                         [messageBody.text stringByAppendingString:@"\n"], kSKPSMTPPartMessageKey,
                                         @"quoted-printable", kSKPSMTPPartContentTransferEncodingKey,
                                         nil];
        [parts_to_send addObject:plain_text_part];

        // to send attachment

        NSString *image_path = [[NSBundle mainBundle] pathForResource:BookCover ofType:@"jpg"];
        NSData *image_data = [NSData dataWithContentsOfFile:image_path];        
        NSDictionary *image_part = [NSDictionary dictionaryWithObjectsAndKeys:
                                    @"inline;\r\n\tfilename=\"image.png\"",kSKPSMTPPartContentDispositionKey,
                                    @"base64",kSKPSMTPPartContentTransferEncodingKey,
                                    @"image/png;\r\n\tname=Success.png;\r\n\tx-unix-mode=0666",kSKPSMTPPartContentTypeKey,
                                    [image_data encodeWrappedBase64ForData],kSKPSMTPPartMessageKey,
                                    nil];


        [parts_to_send addObject:image_part];



        test_smtp_message.parts = parts_to_send;

        Spinner.hidden = NO;
        [Spinner startAnimating];
        ProgressBar.hidden = NO;
        HighestState = 0;

        [test_smtp_message send];

    }

}else {
    UIAlertView *alertNoconnection = [[UIAlertView alloc] initWithTitle:@"?????" message:@"?? ???? ???? " delegate:self cancelButtonTitle:@"?????" otherButtonTitles:nil, nil];
    [alertNoconnection show];
}
}

but when I tried to send it gives me the following Exception:

 *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSCFString appendString:]: nil argument'

and it highlighted this line in SKPSMTPMessage.m

 [message appendString:[part objectForKey:kSKPSMTPPartMessageKey]];

and I Can't understand what is nil exactly Can Anyone help me in this issue? Thanks in Advance.