When dnn exception occured and if visul studio debugger was attached to dnn it used to show in visual studio exact source code location of error, it put breakpoint there. now it stopped working. anyone knows how do i reenable it? watching event log is time consuming and sometimes i cant even see the true error there.

Sorry I realized this is not dnn problem but asp.net/visual studio problem. Solution is to enable break on exception in visual studio (debug->exceptions):

http://msdn.microsoft.com/en-us/library/aa290821%28v=vs.71%29.aspx