Android Question Error In Placing a Call..From my App..when download from Play Store..

Hi ,
I have make an app in which two label displaying the phone number....there is two button also by which we can place a call on the numbers displayed in Label.
Its works ok....when I install app with unknown sources.....but after downloading from PLAY Store
it show error..java.lang.SecurityExceptionermission Denial:Starting Intent{act=andriod.intent.action.CALL dat=tel:xxxxxxxxxx flg=0x20000 cmp=com.andriod.server.telecom/.component.UserActivity}
Screenshot is attached.
please tell me where i am doing wrong. This is my first app.