iOS exception in pushViewController - objective-c

Question

I'm trying to create an NSMutableArray of ModuleViewControllers (which inherits from UIViewController) in order to open a given view from a given button. The ModuleViewController is also described in ModuleViewController.xib
So I load a list of module xml files and pass them, one by one, to a constructor (which ignores them atm) and then add the result to an NSMutableArray.
The problem happens when I try to push the view controller. I get a SIGABRT/exception and I'm not sure why. Any ideas?
Failed Call:
-(IBAction) buttonPressed:(id)sender {
ModuleViewController *module = [moduleVCList objectAtIndex:[sender tag]];
[[self navigationController] pushViewController:module animated:YES];
}
Constructor Call:
[moduleVCList addObject:
[[ModuleViewController alloc] initWithXMLName:[module objectForKey:#"file"]]];
Constructor:
- (id)initWithXMLName:(NSString *)xmlName {
self = [super initWithNibName:#"ModuleViewController" bundle:nil];
if (self) {
}
return self;
}
Backtrace:
#0 0x01867cf0 in objc_exception_throw ()
#1 0x0167ea78 in +[NSException raise:format:arguments:] ()
#2 0x0167e9e9 in +[NSException raise:format:] ()
#3 0x00209f0d in -[UIViewController _loadViewFromNibNamed:bundle:] ()
#4 0x0020a3a9 in -[UIViewController loadView] ()
#5 0x0020a5cb in -[UIViewController view] ()
#6 0x0020a941 in -[UIViewController contentScrollView] ()
#7 0x0021c47d in -[UINavigationController _computeAndApplyScrollContentInsetDeltaForViewController:] ()
#8 0x0021c66f in -[UINavigationController _layoutViewController:] ()
#9 0x0021c93b in -[UINavigationController _startTransition:fromViewController:toViewController:] ()
#10 0x0021d3df in -[UINavigationController _startDeferredTransitionIfNeeded] ()
#11 0x0021d986 in -[UINavigationController pushViewController:transition:forceImmediate:] ()
#12 0x0021d5a4 in -[UINavigationController pushViewController:animated:] ()
#13 0x00003c1a in -[MainViewController buttonPressed:] (self=0x6a283d0, _cmd=0xb874, sender=0x6a286c0) at *snip*/MainViewController.m:149
#14 0x016d7ec9 in -[NSObject performSelector:withObject:withObject:] ()
#15 0x001475c2 in -[UIApplication sendAction:to:from:forEvent:] ()
#16 0x0014755a in -[UIApplication sendAction:toTarget:fromSender:forEvent:] ()
#17 0x001ecb76 in -[UIControl sendAction:to:forEvent:] ()
#18 0x001ed03f in -[UIControl(Internal) _sendActionsForEvents:withEvent:] ()
#19 0x001ec2fe in -[UIControl touchesEnded:withEvent:] ()
#20 0x0016ca30 in -[UIWindow _sendTouchesForEvent:] ()
#21 0x0016cc56 in -[UIWindow sendEvent:] ()
#22 0x00153384 in -[UIApplication sendEvent:] ()
#23 0x00146aa9 in _UIApplicationHandleEvent ()
#24 0x015c0fa9 in PurpleEventCallback ()
#25 0x016aa1c5 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ ()
#26 0x0160f022 in __CFRunLoopDoSource1 ()
#27 0x0160d90a in __CFRunLoopRun ()
#28 0x0160cdb4 in CFRunLoopRunSpecific ()
#29 0x0160cccb in CFRunLoopRunInMode ()
#30 0x015bf879 in GSEventRunModal ()
#31 0x015bf93e in GSEventRun ()
#32 0x00144a9b in UIApplicationMain ()
#33 0x00002862 in main (argc=1, argv=0xbfffedc8) at *snip*/main.m:16
#34 0x000027d5 in start ()