'NSException' Error, Crashes after pressing rectangle button - Cocoa Touch

I've made a rectangle button, which, when the user taps it they go to their iPod.

I get this error once I press the button when debugging. I've checked thoroughly on the iPod code and everything seems to be correct.

Here is the error from the debugger called after throwing an instance of NSException:

2011-04-23 18:42:11.580 iApp[1197:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSURL initFileURLWithPath:]: nil string parameter'
*** Call stack at first throw:
(
    0   CoreFoundation                      0x01369be9 __exceptionPreprocess + 185
    1   libobjc.A.dylib                     0x0115e5c2 objc_exception_throw + 47
    2   CoreFoundation                      0x01322628 +[NSException raise:format:arguments:] + 136
    3   CoreFoundation                      0x0132259a +[NSException raise:format:] + 58
    4   Foundation                          0x00065b12 -[NSURL(NSURL) initFileURLWithPath:] + 90
    5   iApp                             0x000056f3 -[MainViewController setupApplicationAudio] + 148
    6   iApp                             0x00005af0 -[MainViewController viewDidLoad] + 78
    7   UIKit                               0x0037765e -[UIViewController view] + 179
    8   UIKit                               0x00379012 -[UIViewController viewControllerForRotation] + 63
    9   UIKit                               0x00374f76 -[UIViewController _visibleView] + 90
    10  UIKit                               0x0060ea97 -[UIClientRotationContext initWithClient:toOrientation:duration:andWindow:] + 354
    11  UIKit                               0x002f0ba8 -[UIWindow _setRotatableClient:toOrientation:updateStatusBar:duration:force:] + 954
    12  UIKit                               0x00570948 -[UIWindowController transition:fromViewController:toViewController:target:didEndSelector:] + 1053
    13  UIKit                               0x0037b982 -[UIViewController presentModalViewController:withTransition:] + 3151
    14  iApp                           0x00002330 -[MainerViewController goImport:] + 153
    15  UIKit                               0x002c9a6e -[UIApplication sendAction:to:from:forEvent:] + 119
    16  UIKit                               0x003581b5 -[UIControl sendAction:to:forEvent:] + 67
    17  UIKit                               0x0035a647 -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 527
    18  UIKit                               0x003591f4 -[UIControl touchesEnded:withEvent:] + 458
    19  UIKit                               0x002ee0d1 -[UIWindow _sendTouchesForEvent:] + 567
    20  UIKit                               0x002cf37a -[UIApplication sendEvent:] + 447
    21  UIKit                               0x002d4732 _UIApplicationHandleEvent + 7576
    22  GraphicsServices                    0x01b80a36 PurpleEventCallback + 1550
    23  CoreFoundation                      0x0134b064 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 52
    24  CoreFoundation                      0x012ab6f7 __CFRunLoopDoSource1 + 215
    25  CoreFoundation                      0x012a8983 __CFRunLoopRun + 979
    26  CoreFoundation                      0x012a8240 CFRunLoopRunSpecific + 208
    27  CoreFoundation                      0x012a8161 CFRunLoopRunInMode + 97
    28  GraphicsServices                    0x01b7f268 GSEventRunModal + 217
    29  GraphicsServices                    0x01b7f32d GSEventRun + 115
    30  UIKit                               0x002d842e UIApplicationMain + 1160
    31  iApp                            0x00001b34 main + 102
    32  iApp                             0x00001ac5 start + 53
    33  ???                                 0x00000001 0x0 + 1
)
terminate

If you look at the very first line of your crash report, it states you are passing a nil string to NSURL's initFileURLWithPath method:

'NSInvalidArgumentException', reason: '*** -[NSURL initFileURLWithPath:]: nil string parameter'

From Apple documentation.

Passing nil for this parameter produces an exception.

So make sure to check your NSString before sending to initFileURLWithPath method,

NSURL* targetFileURL = nil ;
if(targetFilePath != nil)
{
       targetFileURL = [[NSURL alloc] initFileURLWithPath:targetFilePath];
}