ASP.Net Application Issues:  Random System.Web.HttpUnhandledException Thrown

Hello

Recently I have installed a ASP.Net application (coded in VB) on site.  At the moment 2 PC's and several wireless hand held devices are used to connect to the website.

Since installing the application we are having several issues:

System.Web.HttpUnhandledException is thrown quite regularly and we cant seem to work out while this happening.  This is thrown at complete random times.  Most of the time this is caught by the Application_Error() function inside of Global.asax.

One person can log into a page and a minute or two later recieve a System.Web.HttpUnhandledException while another user can access and use the page with no problems.  Logging out and back in seems to fix this most times.

We also seen the following error: Timeout expired.  The timeout period elapsed prior to obtaining a connection from the pool.  This may have occurred because all pooled connections were in use and max pool size was reached.

And Object reference not set to an instance of an object.  This seems to be that session variables are somehow lost.

I have tried looking into these issues but at the moment I dont seem to be getting anywhere.  Not sure if this due to application design or something to do with .Net or IIS configuration.

Any help would be great =:)