I have an application that has a application pool that shuts down a couple of times a day and I can't figure out why. the website is hosted on a VM with SQL Server R2. the version of IIS is 7 and the website has a dedicated application pool using .NET framework v4.0.30319.
At the application level the website is using a target framework of 4.5 and seems to run just fine for a 24-48 hour period and then for some reason the application pool just stops. We do have other .NET 4.5 applications running on this machine and their application pools do not have this problem. The only thing slightly different about this application is that we initiate a separate thread to send a order confirmation email when an order is completed. We average about a couple of hundred orders a day for this website.
According to the event log the error reported prior to the shutdown is
"A process serving application pool 'RetailSupport' suffered a fatal communication error with the Windows Process Activation Service"
Please help
I would check, if your code could hit under some circumstances an endless loop or a recursive call of methods. This is often the reason for this error.
What always helps me in such cases is to add debug logs (e.g. log4net) in your case especially before the email is sent, status info about resources, etc. They can be more informative then the IIS logs.
If this does not help, check http://support.microsoft.com/kb/919789/en how to use the debug Diagnostic tool, to get more details for the error.
Look also for IIS: Web Application hangs periodically needs system reboot it could help you.
Also: what recycle strategy on IIS do you have?