iphone App crashes while Parsing

my app is crashed as it execute [NSXMLParser parse]; statement,and

i am getting following :

2011-03-01 09:36:31.735 MasterApp[228:207] -[NSCFString bytes]: unrecognized selector sent to instance 0x5f6b000

2011-03-01 09:36:31.738 MasterApp[228:207] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSCFString bytes]: unrecognized selector sent to instance 0x5f6b000'

* Call stack at first throw:

(

0 CoreFoundation 0x0252eb99 exceptionPreprocess + 185

1 libobjc.A.dylib 0x0267e40e objc_exception_throw + 47

2 CoreFoundation 0x025306ab -[NSObject(NSObject) doesNotRecognizeSelector:] + 187

3 CoreFoundation 0x024a02b6 __forwarding + 966

4 CoreFoundation 0x0249fe72 _CF_forwarding_prep_0 + 50

5 Foundation 0x00114afc -[NSXMLParser parse] + 147

6 MasterApp 0x0000c731 -[identifierList getUrl] + 994

7 MasterApp 0x0000c306 -[identifierList actionSheet:clickedButtonAtIndex:] + 56

8 UIKit 0x0077047d -[UIActionSheet(Private) _buttonClicked:] + 258

9 UIKit 0x002dc7f8 -[UIApplication sendAction:to:from:forEvent:] + 119

10 UIKit 0x00367de0 -[UIControl sendAction:to:forEvent:] + 67

11 UIKit 0x0036a262 -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 527

12 UIKit 0x00368e0f -[UIControl touchesEnded:withEvent:] + 458

13 UIKit 0x003003d0 -[UIWindow _sendTouchesForEvent:] + 567

14 UIKit 0x002e1cb4 -[UIApplication sendEvent:] + 447

15 UIKit 0x002e69bf _UIApplicationHandleEvent + 7672

16 GraphicsServices 0x02d8a822 PurpleEventCallback + 1550

17 CoreFoundation 0x0250fff4 CFRUNLOOP_IS_CALLIN开发者_C百科G_OUT_TO_A_SOURCE1_PERFORM_FUNCTION + 52

18 CoreFoundation 0x02470807 __CFRunLoopDoSource1 + 215

19 CoreFoundation 0x0246da93 __CFRunLoopRun + 979

20 CoreFoundation 0x0246d350 CFRunLoopRunSpecific + 208

21 CoreFoundation 0x0246d271 CFRunLoopRunInMode + 97

22 GraphicsServices 0x02d8900c GSEventRunModal + 217

23 GraphicsServices 0x02d890d1 GSEventRun + 115

24 UIKit 0x002eaaf2 UIApplicationMain + 1160

25 MasterApp 0x00001dbc main + 102

26 MasterApp 0x00001d4d start + 53

)

terminate called after throwing an instance of 'NSException'

Program received signal: “SIGABRT”.

thank you in advance

i just try to use "urlData" instead of webData in xmlParser = [[NSXMLParser alloc] initWithData:urlData]; and now it parse very well