I decided to post this question also here in case the issues we have is related to sql server.
There is a problem that bother me for some time. I have an asp.net mvc that uses NHibernate for modeling the database. The infrastructure is the following: Windows 2008 R2 for all virtual machines. IIS 7.5 is working on one virtual machine. Sql Server 2008 is working on another virtual machine. We have couple of databases, two that stores application data and one that registers all unhandled exceptions.
Sometimes virtual machine that hosts database server restarts (in the middle of the night, not quite sure about the reason) after that connection to the databases that stores application data is not working and as result there are thousands of unhandled exceptions that get registered in the third database. Important to mention that databases are accessible from Management Studio. The problem is solved by resetting IIS. Connetion are handled via NHibernateUtil class which opens and closes session at each request.