android : error in datepicker -

i using link provide date picker in android app

but getting error:

05-21 10:19:08.712: e/androidruntime(13265): android.view.windowmanager$badtokenexception: unable add window         -- token android.app.localactivitymanager$localactivityrecord@40d42048 not valid; activity running? 05-21 10:19:08.712: e/androidruntime(13265):    @ android.view.viewrootimpl.setview(viewrootimpl.java:567) 05-21 10:19:08.712: e/androidruntime(13265):    @ android.view.windowmanagerglobal.addview(windowmanagerglobal.java:246) 05-21 10:19:08.712: e/androidruntime(13265):    @ android.view.windowmanagerimpl.addview(windowmanagerimpl.java:69) 05-21 10:19:08.712: e/androidruntime(13265):    @ android.app.dialog.show(dialog.java:281) 05-21 10:19:08.712: e/androidruntime(13265):    @ android.app.activity.showdialog(activity.java:3071) 05-21 10:19:08.712: e/androidruntime(13265):    @ android.app.activity.showdialog(activity.java:3021) 

how resolve error??? please help!!!

heres java code:

public class applicant extends activitygroup {  private int myear; private int mmonth; private int mday; static final int date_dialog_id = 1;   @override     protected dialog oncreatedialog(int id) {         switch (id) {          case date_dialog_id:             return new datepickerdialog(this,                 mdatesetlistener,                 myear, mmonth, mday);         }         return null;     }     protected void onpreparedialog(int id, dialog dialog) {         switch (id) {          case date_dialog_id:             ((datepickerdialog) dialog).updatedate(myear, mmonth, mday);             break;         }     }         private void updatedisplay() {         tv_dob.settext(             new stringbuilder()             // month 0 based add 1             .append(mmonth + 1).append("-")             .append(mday).append("-")             .append(myear).append(" "));     }     private datepickerdialog.ondatesetlistener mdatesetlistener =         new datepickerdialog.ondatesetlistener() {          public void ondateset(datepicker view, int year, int monthofyear,                 int dayofmonth) {             myear = year;             mmonth = monthofyear;             mday = dayofmonth;             updatedisplay();         }     };   arraylist<string> city=new arraylist<string>();  edittext applicatn_formno,fname,mname,lname,addrs1,addrs2,landmrk, pincode,stdcode,telephone,mobile;   button btn_next,pickdate;  spinner spin_occupation;  textview tv_dob,tv_applndate;  public void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.applicant);      spin_occupation=(spinner)findviewbyid(r.id.spinner_ocupa);      tv_dob=(textview)findviewbyid(r.id.edt_dateofbirth);     tv_applndate=(textview)findviewbyid(r.id.applndate);      pickdate=(button)findviewbyid(r.id.pickdate);        current_date=dateformat.getdatetimeinstance().format(new date());     tv_applndate.settext(current_date);      pickdate.setonclicklistener(new view.onclicklistener() {         @suppresswarnings("deprecation")         public void onclick(view v) {             showdialog(date_dialog_id);         }     });      final calendar c = calendar.getinstance();     myear = c.get(calendar.year);     mmonth = c.get(calendar.month);     mday = c.get(calendar.day_of_month);     updatedisplay();       btn_next.setonclicklistener(new onclicklistener() {          @override         public void onclick(view v) {             // todo auto-generated method stub              //toast.maketext(getapplicationcontext(), ""+ str_state, toast.length_long).show();               if(str_permant.equalsignorecase("no"))             {                 intent activity=new intent(v.getcontext(),permanentaddress.class);                 replacecontentview("activity", activity);             }             else{                 intent activity2=new intent(v.getcontext(),applicant2.class);                 replacecontentview("activity2", activity2);             }         }     });  } 

} xml file(this relevant code datepicker)

   <relativelayout         android:layout_width="fill_parent"         android:layout_height="wrap_content"         android:layout_margintop="10dp" >          <button             android:id="@+id/pickdate"             android:layout_width="25dp"             android:layout_height="25dp"             android:layout_marginleft="5dp"             android:layout_torightof="@+id/edt_dateofbirth"             android:background="@drawable/calendaricon" />          <textview             android:id="@+id/edt_dateofbirth"             android:layout_width="wrap_content"             android:layout_height="wrap_content"             android:layout_alignparentleft="true"             android:layout_alignparenttop="true"             android:text="date of birth"             android:textsize="14sp" />      </relativelayout>