Monotouch Application fatal error - iphone

Question

I am trying to understand the reason my app crashes, randomly it seems, when trying to present a view.
The button click code:
if ( d.rootNavigationController.RespondsToSelector(
new MonoTouch.ObjCRuntime.Selector("presentViewController:animated:completion:")))
{
d.rootNavigationController.PresentViewController(childBroswer, true,null);
}
else
{
d.rootNavigationController.PresentModalViewController(childBroswer, true);
}
This is the stack trace:
at MonoTouch.UIKit.UIApplication.Main (string[],string,string) [0x0004c] in /Developer/MonoTouch/Source/monotouch/src/UIKit/UIApplication.cs:38
at appname.Application.Main (string[]) [0x00000] in /Users/us/Projects/appname/appname/Main.cs:17
at (wrapper runtime-invoke) object.runtime_invoke_dynamic (intptr,intptr,intptr,intptr) <0xffffffff>
Native stacktrace:
0 appname 0x00a81ba9 mono_handle_native_sigsegv + 244
1 appname 0x00a48015 mono_sigsegv_signal_handler + 172
2 libsystem_c.dylib 0x35df3e93 _sigtramp + 42
3 UIKit 0x33f820a5 <redacted> + 72
4 UIKit 0x33f82057 <redacted> + 30
5 UIKit 0x33f82035 <redacted> + 44
6 UIKit 0x33f818eb <redacted> + 502
7 UIKit 0x33f81de1 <redacted> + 488
8 UIKit 0x33ea0421 <redacted> + 5768
9 CoreFoundation 0x3ad3a6cd <redacted> + 20
10 CoreFoundation 0x3ad389c1 <redacted> + 276
11 CoreFoundation 0x3ad38d17 <redacted> + 742
12 CoreFoundation 0x3acabebd CFRunLoopRunSpecific + 356
13 CoreFoundation 0x3acabd49 CFRunLoopRunInMode + 104
14 GraphicsServices 0x390792eb GSEventRunModal + 74
15 UIKit 0x33eeb2f9 UIApplicationMain + 1120
16 appname 0x0006f618 wrapper_managed_to_native_MonoTouch_UIKit_UIApplication_UIApplicationMain_int_string___intptr_intptr + 240
17 appname 0x009bdb20 appname_Application_Main_string__ + 152
18 appname 0x0068664c wrapper_runtime_invoke_object_runtime_invoke_dynamic_intptr_intptr_intptr_intptr + 200
19 appname 0x00a4962f mono_jit_runtime_invoke + 1054
20 appname 0x00aa5df3 mono_runtime_invoke + 90
21 appname 0x00aa88d7 mono_runtime_exec_main + 306
22 appname 0x00aabb5b mono_runtime_run_main + 482
23 appname 0x00a5c133 mono_jit_exec + 94
24 appname 0x00ae9e3c main + 2220
25 appname 0x00002028 start + 40
Got a SIGSEGV while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries
used by your application.
Any ideas what is the error?
Thanks!