Auto restart application failed in iis

Question

Hi there, 

  Hope all are fine. here i face  a problem in iis Manager 6.0. I have developed a scheduled mail application using asp.net c# which will mail daily. In application_start in global.asax  a code for mailing is written(To say application started). 

Now the problem is when i restart the iis , the application failed to start. It only work when i manually open the page. I also changed the startup mode of defaultapp pool from "on demand" to "always running" . still i am facing the problem. please solve this.....