Thank you Guys to give me many suggestions. Finally I got a solution. That is i have started the NetErrorPage intent two times. One time, i have checked the net connection availability and started the intent in page started event. second time, if the page has error, then i have started the intent in OnReceivedError event. So the first time dialog is not closed, before that the second dialog is called. So that i got a error.
Reason for the Error: I have called the showInfoMessageDialog method
two times before closing the first one.
Now I have removed the second call and Cleared error :-).