ASP.net information event "Application compilation is starting"

Question

Hi all:

We use MSMQ to capture all the event thrown by our asp.net site and store the data into our database. Throughout the day, we can see the event id "1003" with Title = "Application compilation is starting" in our logging database. However, we don't see the corresponding event 1004 which is "Application compilation ends". I was wondering what could possibly cause this? We deploy our site with the precompiled option (update allow) and we have a very high use of session object (bad I know!). Do the message indicates our web app is restarting on its own?

Thanks, Herman