i have cought the problem
in my project properties the debug section there are three options in enable debugers:
-enable unmanaged code debugging
-enable sql server debugging
-enable the visual studio hosting process
if i enable 2nd or 3rd option the program works fine but hangs exactly at 12th minute.
if i enable 1st option then the program never stops but it works very slow...
i think there is problem related to debugging process..
how can i do this that my application runs normally wiout stoping after 12 mins
thanks!