windows phone 7 - How to navigate to a login page instead of MainPage -

i'm in sticky position. have published app , have been receiving crash reports. of invalidoperationexception. 19 frames in stacktrace shows internal functions , hence im not able figure out function raised it. lot of debugging, think invalidoperation exception caused way redirect navigation login page.

the basic operation this. if user has set password, navigates password page else mainpage. code follows

app() {    // usual code    rootframe.navigating += new navigatingcanceleventhandler(rootframe_navigating); }   void rootframe_navigating(object sender, navigatingcanceleventargs e) {         if (e.uri.tostring().contains("/rootpage.xaml") != true)             return;          cyclemanager pcycman = cyclemanager.instance;          e.cancel = true;         rootframe.dispatcher.begininvoke(delegate         {             if (pcycman.getpasswordenabled())                 rootframe.navigate(new uri("/passwordpage.xaml", urikind.relative));             else                 rootframe.navigate(new uri("/mainpage.xaml", urikind.relative));         }); } 

the rootpage mentioned above defined in <app> tag in wmappmanifest.xml

<tasks>   <defaulttask name="_default" navigationpage="rootpage.xaml" /> </tasks> 

when debugged above codes, found same call stack stacktrace. tell me if correct method of navigating page other mainpage? have included stacktrace below

"frame    image             function                                                offset     0        coredll.dll       xxx_raiseexception                                      19         1        mscoree3_7.dll                                                            436488     2        mscoree3_7.dll                                                            386545     3        mscoree3_7.dll                                                            540936     4                          transitionstub                                          0          5                          system.windows.navigation.navigationservice.navigate    1580       6                          system.windows.controls.frame.navigate                  80         7                          .__c__displayclass5._application_activated_b__3         136        8        mscoree3_7.dll                                                            429164     9        mscoree3_7.dll                                                            185803     10       mscoree3_7.dll                                                            84423     11                         system.reflection.runtimemethodinfo.internalinvoke      112        12                         system.reflection.runtimemethodinfo.internalinvoke      1564       13                         system.reflection.methodbase.invoke                     104        14                         system.delegate.dynamicinvokeone                        564       15                         system.multicastdelegate.dynamicinvokeimpl              84         16                         system.windows.threading.dispatcheroperation.invoke     80         17                         system.windows.threading.dispatcher.dispatch            404        18                         system.windows.threading.dispatcher.oninvoke            56         19                         system.windows.hosting.callbackcookie.invoke            84" 

thanks patience in reading such long question.

to control navigation can achieve this.

get urimapper app.xaml resources, , assign root frame

urimapper mapper = resources["mapper"] urimapper; rootframe.urimapper = mapper; 

and update mapper appropriate

if (ispasswordsaved)                 mapper.urimappings[0].mappeduri = new uri("/passwordpage.xaml?method=urimapper", urikind.relative);             else                 mapper.urimappings[0].mappeduri = new uri("/mainpage.xaml?method=urimapper", urikind.relative);